Hexerin

You do, in fact, remember correctly. WitW must be completed before the slots show up.

There's no way to do so, you just have to do the test. Not sure why you think you can't do your test though, as they're all fairly simple and relatively easy. Most also have ways to cheese them, further trivializing them.

Tell us you know nothing about Voruna, without telling us you know nothing of Voruna.
To start with, I'll directly answer your questions:
This is the build I use, which is mostly (if not entirely) min/max'd. It is also SP Endurance viable, all the way to level 9,999 (level cap).
Primed/Archon mods are not required. Primed Flow just gives additional wiggle room on energy econ (not that she hurts for energy in the first place), while the Archon mods are mostly a "why not?" kind of deal. Operator school is mandated to Unairu against Grineer, because you need the armor strip for the first few kills. The shield strip can help against Corpus, but it isn't necessary. Archon shards are entirely preference, I'd personally recommend ability duration for comfort.
The game flow is simple:
Pop energy pizza to get energy topped off at the start of mission (optional, but negates any RNG weirdness of early energy econ). Enter Ulfrun's Descent, and then go find your first enemies. Activate Shroud of Dynar and Lycath's Hunt. Lunge at a target with Fangs of Raksh. If you're fighting Grineer, pop out into Operator and strip their armor first. This is only needed for the first few kills, to build your Ulfrun's Descent multiplier to the max (10x). Rip their throat out with Ulfrun's Descent, which will be: Doubled by Shroud of Dynar. Then that result is doubled again because of the debuffs from Fangs of Raksh. Only hit each enemy once with an Ulfrun's Descent lunge. The slash proc from it will kill anything in the game. Enemies that are immune to slash procs are, unfortunately, not things you can kill. Ignore them entirely. Some weaker ones can potentially be killed by the impact damage, however. Once you've gotten Molt Augmented to its full 250 stacks (+60% ability strength), refresh Ulfrun's Descent. You can also do so at any time before then, if you so desire. Keep Shroud of Dynar active at all times (Lycath's Hunt is refreshed by Fangs of Raksh). Try to ensure you're doing so while at full Molt Efficiency stacks (+36% ability duration). Always hit your target with Fangs of Raksh first, so that you get the doubled doubling on Ulfrun's Descent lunges.
You'll never have to leave Ulfrun's Descent, and once you get good at it, you'll be able to reach really high KPM (kills per minute) which satisfies the needs of modes like Survival. Enemies can't effectively attack you due to Shroud of Dynar, but even if you get hit with a stray shot, it'll simply pop your shields (which you reset with Brief Respite on your next Shroud/Fangs).
Your other equipment (primary, secondary, melee, etc) are completely irrelevant. Voruna is really good for Nightwave challenges that involve taking specific equipment, for this reason. She's also good if you want to passively raise mastery on things, although that only applies if you're playing in a squad of course (all of your own kills will be 100% affinity to warframe, due to Ulfrun's Descent being an ability of course).
Lastly, one parting note. If you've encountered a Corpus Nullifier that's blocking forward progress, there's no need to exit Ulfrun's Descent. Just hop out to Operator, and blast the shield down with your amp. High rate of fire amps (7xx, for example) are best at this, of course.
Actually, one more last thing. When I was originally learning Voruna, TheKengineer's vids were an invaluable resource. If you'd also like to have that additional context, I'm putting them here for you:
 

That stats screen is infamous for breaking and thereafter showing incorrect values. Open your menu, go to profile, then logout. Upon logging back in, the UI generally is fixed. You can test by entering your melee weapon mod loadout, exiting, and then re-entering. If it shows positive/negative changes, then the UI is still broken, and you'll have to completely relaunch the game to fix it. These fixes are only temporary though, so get used to doing them.

This. However, bear in mind that the Mother pods out in the field are:
Tied to that specific vault tier. There's three tiers, so three Mother pods. The bounties from Mother out in the field are "Arcana" vault bounties. You don't have to unlock the vault again, but you also don't get to fight its Necramech(s). Any loot containers you broke, any secret areas you unlocked, and the deep vault (passcode after Loid escort quest) do not reset. If you want to get fresh vaults (which is what you want if you're still progressing Necraloid), you'll have to return to the Necralisk and generate a new Cambion Drift instance. This is because the only way to progress Necraloid is with the matrices, which are dropped by the Necramechs (that don't respawn).

There's not really any particular focus needed, Djinn only has access to a single CC ability (which it comes with, so no need to farm/buy either). Weapon choice isn't relevant / personal preference, but if you're just looking for the meta then Helstrum (available via Fortuna, link) is the obvious choice.
Djinn build, 3 forma needed:
Helstrum build, 1 forma needed:

You obtain extractor deployment slots at:
Mastery rank 0 Mastery rank 5 Mastery rank 10 Prime Access Only the first time you purchase it. Tier is irrelevant, even just the accessories tier will provide the slot. Prime Vault and Prime Resurgence are not the same thing, and do not count. Being a founder. Obviously unobtainable now. So for F2P players, you will cap out at 3 slots. For those who have ever picked up something from Prime Access, you'll have a 4th slot. Only founders can have 5 slots.