There's some sound advice here already, so allow me to re-iterate on it a little, with some more on top.
If you're coming back after years away, and only have a few max-ranked items, then this is the perfect point to treat the game as a 'New Game +' situation.
Your priorities are as follows:
1. Complete the Star Chart in regular order.
2. Get the mods you need.
3. Get your Arsenal cooking.
5. Learn about the new systems.
So here we go!
Priority 1. Complete the Star Chart.
This is at once simple, and at the same time an actual journey. The Star Chart has been reworked so you have an actual path of progression through it. Completing missions unlocks new ones, completing objectives allows you to complete Junction missions and unlock planets that you might not have before.
Quests are on the way, with many Junctions giving you the key to start a Quest, and the next Junction requiring you to have finished it. All of the Quests in the Star Chart progression are essential and will unlock newer (to you) functions, like companions, Archwing, the Open Landscapes and so on through.
An important note: If you do not have the mods, gear and frames for it, the Open Landscapes of The Plains of Eidolon, The Orb Vallis and The Cambion Drift (Earth, Venus and Deimos, respectively) will not be easy for you and will not actually give you the decent rewards. Complete the introduction missions on them and progress through the Star Chart for more essential things. Then come back to these places later to grind out the actual content.
I would suggest coming back to Cetus, the Plains of Eidolon, after completing the quest The War Within, because it will unlock a new Syndicate and something that is very useful in the later Quests (like The Chains of Harrow), and I genuinely advise grinding that new thing up a bit in order to make those quests a heck of a lot easier.
To round this part out, any Warframe with a half-decent build on it, with any weapon that has the similar basic mods, will complete the Star Chart, it is not designed to be punishing or all that difficult. That's why I say to get it done first.
Priority 2. Getting the mods.
On your journey you'll have unlocked a lot of areas to grind mods. Completing all the nodes on a planet unlocks Nightmare missions (one is present on every planet and cycles every 8 hours (meaning you can do one per planet per game session). Grind these, level them up, they are almost always useful.
On Deimos (what used to be the Derelict) the mission nodes will all have hidden Vaults in them, craft Dragon Keys (you get the blueprints from the Dojo in the Orokin Lab, the blueprints are infinite and you can craft as many as you like if you have resources), use them to unlock the Vaults for Corrupted Mods. These are incredible for min-maxing and plenty of builds use at least one of them.
Once you have completed the Star Chart you will unlock the Arbitration game mode, this also has very useful mods, and is also a great source of the resource you use to rank up mods, Endo, so grind that when you can.
For any mod you see in a player's build that you don't have, look to the Wiki for where it drops and go find it. While many mods are niche and generally not worth picking over others, the core ones are important.
And, failing all that, you can actually buy many of the core mods in the Market now as dedicated packs. Base damage, Elemental Damage and so on.
Priority 3. Expanding your Arsenal.
The bosses along the Star Chart drop some pretty good frames. Some Quests have them. Your Dojo has discount frames that are very, very useful.
For a new starter the frames to look for include Rhino (from the Venus boss) the tanky boi, Volt from the Dojo for a versatile boi, Nezha from the Dojo for a faster tanky boi with some great team support, Zephyr from the Dojo for a combo of area denial and damage...
You'll pick up Nekros from the boss on Deimos (not the open landscape) for farming parts, Mag comes from the Sargeant on Phobos, Frost from Ceres, Valkyr from Jupiter, Nova from Europa, Ember from Saturn, Equinox is one of the annoying grinds from Uranus, Chroma will have been gained in quests by now, Loki from Neptune, Trinity from Pluto, Saryn from Sedna and finally Atlas from Eris.
Quests you get along the way will give you Limbo, Mirage, Revenant, Harrow, Inaros, Titania, Octavia, Protea and Mesa.
That's a lot to take in, but those frames will genuinely set you up for nearly everything you encounter in the game. Find them, level them.
There are more, but they'll come from things like the syndicates you find in Cetus, Fortuna and the Necralisk. They'll take you a while, and you don't need them over anything else, but they are nice to have.
Weapons can be grabbed in the same way, some bosses drop parts, the Dojo has literally dozens, some you can just get the Blueprints from the Market for Credits.
Primes are a huge thing, there are now 33 Prime Warframes in the game, with an average of two Prime Weapons each, and a much easier way to get them than originally, because you can go in public for short runs (or longer ones if you like that format) and get more rolls of the dice at the outcome. Just be sure to pay attention to the Relics you pick up over the course of completing the Star Chart. It may take a little while, but finding some friends for dedicated farming sessions will make this a lot easier.
You can also get weapons from Syndicates, pay attention to them as they include some very good upgrades to ones you might already like.
Melee weapons are incredibly powerful under the current system, and some good modding of those will see you a long, long way in the game.
It's time to grind things to trade for Platinum, though, because without Plat you can't unlock the Arsenal Slots to store your growing stable and have space for all those guns and swords.
Priority 4. Forma.
I wish, I wish, I wish that somebody had told me how much of this I was going to use over time. I would guess that I average 3 per Weapon, and 4 per Warframe.
That adds up over time. With some weapons and Forma-applicable items even having to use 5 Forma just to get the maximum Mastery Points unlocked from them.
Think about that. At 4 Forma per Warframe, we have 47 base Warframes and 33 Primes, meaning that a complete collection for Mastery Ranking will use an average of 320 Forma.
You can now build one Forma in the Foundry over 23 hours (so that you can play at the same time every day and claim them). Meaning 1 per day. That's nearly a year just to fill out your Frames. Let alone the literal 300+ Weapons.
Use the Relics you've found to get Prime Parts, but build every single Forma you unlock from those. Get Forma from every Alert you can see. Use Events like the current Plague Star (which you're under-equipped for, best wait for next time) to gain Forma quickly. Anything. Even trade some of your excess Prime Parts for Platinum and buy it in Bundles of 3 for 35p (way better value than 1 for 20p, which is the base).
Forma is essential.
Get it at every opportunity.
Priority 5. Learn the new Systems.
This I'm not equipped to go through, I haven't the time to explain them all. I may not be able to write them all out.
But... here's a sample.
The basic Modding system, what interacts with what, how mods affect Warframes and Weapons based on the raw stats, and how they interact with the current damage system.
The current Damage System. This has undergone changes, with Elemental damage and Status effects, even Critical Hits having undergone some updates over time. Mods that make use of all of these, weapons that have special interactions with the damage they deal... There are tutorials, or a lot of reading, but it's something important to how you mod, how you play, and what gear/frames/weapons you take to the different missions.
New Mission types that have arrived since you left.
Endo replacing Mod Fusion. Clear goals to work towards.
Relics replacing Void Keys. In this one, try to avoid bias from the people talking, try to stick to the facts only, it's divisive.
Arcanes for Warframes and Weapons.
The introduction of Railjack in the Empyrean system.
How Open Landscape Bounties and Syndicates work.
The Syndicates themselves.
Unique modding that comes from higher level content, such as the Steel Path giving you Arcanes, or Arbitrations giving you Galvanised Mods.
Literal Spoiler-laden systems I can't give away until you unlock them...
The list just keeps going.
But remember, the Wiki is your friend. Players are always updating it, giving you the tutorials there that you might not get anywhere else. Youtube has plenty of players who will give guides for everything from beginners to the hardcore build-crafters.
Just ask here again if there's something you really, really can't understand, too.
To sum up...
Yeah, priorities are there.
Some are more essential to getting yourself prepped for the higher level content, some are more essential to basic quality of life.
The more you have, in Warframe, the better equipped you are to handle anything they throw at you.
But honestly? Have fun.
Just play the game, keeping in mind those basic goals, and you're going to have a pretty good time of it.
The only mods that don't work on weapons with a pure or combined Elemental damage type, like the Ignis, are mods that affect Impact, Puncture and Slash.
When you add an Elemental mod to any gun, it gives you an additional damage type. But if the weapon has no Impact, for example, adding an Impact mod does not give you a new damage type of Impact, it does absolutely nothing.
So, as Zeku above me has said, use any of the mods that would normally be supported by the weapon. Ignis Wraith, can support the 'base damage' mods, like Serration. It supports Multishot mods like Split Chamber. It will support your Crit mods, like Point Strike and Vital Sense. And it will support your Elemental mods, like Cryo Rounds and Infected clip, or even Rime Rounds and Malignant Force.
If you have an Exilus Adapter, then opening up that slot and using Sinister Reach is a good one, because it increases the range of your flame for hitting enemies further away, although grinding the Plains of Eidolon to get the mod Vigilante Supplies is also worth it because it's a mod that does Ammo Conversion (meaning you don't run out of ammo because all the other types of ammo are converted for it) and it will occasionally (5% at base, but increasing as you put more of the Set mods on your build, like Vigilante Armaments) upgrade your Critical chance by a flat 100%. This turns a regular Yellow crit into an Orange, or an Orange crit into a Red, both of these adding more multiplier to your Critical Damage.
People have been using the Ignis Wraith to great effect since it first came out, so if you head on over to Overframe.gg there will be plenty of builds for you to look through and see how other people mod it.