As others have stated, Prime Access gets you the newest Prime Warframe, prime weapons, and cosmetics. You can also purchase the current Prime Vault, which gives you up to 2 vaulted frames, weapons, and cosmetics. Alternatively, you can farm for relics, then open them for a chance for the blueprints to build the prime warframes or weapons. The vaulted relics only drop in the void and take a while to farm. Finally, you could just trade with other players (often with plat) for the parts. An equinox prime seems to be going for about 100 plat right now on warframe.market. Prime warframes are released every 3 months or so, but Wisp won't be primed for a long time since there are quite a few warframes in line before her.
I use lots of frames and have lots of loadouts. It's really hard for me to pick a favorite...if I had to, I'd go with Oberon Prime. He's great solo, great in a team, has both offense and defense, and is nigh indestructible. Honorable mentions to Frost, Limbo, Baruuk, and Trinity. Favorite primaries: Shotgun: Sobek. Fell in love early on and never let go. Rifle: Supra Vandal. Assault rifle that hits hard and gives me energy. Sniper: Vectis Prime. Favorite secondary: Furis with augment or pyranna prime. Favorite melee: Dark split sword. When I first started I saw that this had one of the highest damage of all the dual blades, so I wanted it. The clan I was in had very little research, so I gathered everything for the sword myself. Stuck with it. Favorite companion: carrier prime.