Im a relatively new player to Warframe (~18 hours played) and I just got my first lvl. 30 frame - Vauban
Vauban? Whaaat. Bought with plat? (aka potato pre-installed)
After defeating Vor, where does the story go?
No story, just gameplay. Enjoy it :D
In regards to my mods, Im working on improving them but I still havent found an aura mod / Orokin Reactor BP. Are these items rare or is this just RNG at work?
Aura mods and Orokin Reactor BPs only drop from alerts. Auras (as far as i can tell) are random, and reactors OR cataylsts come up after dev streams (which are generally every 2 weeks or so?)
I've heard of people selling weapons when they max them out - why? You have a limited number of weapon slots. Once you max a weapon, especially if it isn't very good, you've already gotten all the mastery you can get out of it so it's just occupying space. You want to reserve a few slots for your best weapons, and use 1-2 slots just cycling out mastery weapons/frames.
My rank currently level 2, does affinity affect my ability to rank-up and if so how do I improve it?
Affinity gives you levels in weapons & frames, and levels give you mastery. mastery lets you rank up
General Advice:
Mods are important. You want to fuse cores into things like serration/hornet strike/pressure point as well as elemental mods (cryo rounds, stormbringer, etc)
AS far as your underpowered feeling goes, Vauban (potatoed) should be viable pretty much anywhere. You just need good mods. You'll want to get and max the primary warframe mods quickly (the ones that affect powers, like stretch and streamline and continuity. The corrupted ones can wait until you can handle it). Personally i'd recommend looking at the wiki's article for vauban and then seeing which mods (stretch, etc) affect which abilities. Pick one to focus on, and think through the logical process of making that ability better. Being able to figure this out will help a lot, because while online builds can give you a good start, i think this game is a lot more fun when you personalize your builds and do what you want.
You can always friend me (nadir042) on warframe (PC), or PM me questions about anything.