1. Yeah no storylines except the rarely real same old pre-fight "I'm gonna kill him" stuff that doesn't even mean anything anymore. As much as a lot of the O.G. MMA guys hate the new "TUF-ers" maybe watch some of the earlier seasons of The Ultimate Fighter. There's some good stuff on there and it will satisfy your want of a narrative and give you a foot in the door on finding some fighters you like. Most of the later seasons have been pretty bland, I stopped watching until the last one where they introduced women, they really showed up the men in every way and made the show fresh again.
I found my way into watching a lot of MMA by starting at the beginning. Watch UFC 1 and just bathe in the brutality for a while, follow it along as it evolves. By the time it gets to the late teens it's very close to how it is now so you don't have to watch too many. Some fights run extremely long though and can be boring.
2. This is incredibly subjective, and there's a huge list. Do you find the grappling more interesting, the striking? Someone who just comes to throw down, or the real calculated pro? Do you know enough about the MMA game to recognize and appreciate the subtle skills that someone with real talent brings to the fight or maybe you're all about the intensity and grit someone can bring to the ring.
3. To be honest it's pretty much just the UFC, though I really liked Pride. Once you've gotten into it maybe spend some time watching the old Pride FC shows, the rule differences make the two very different and interesting to think about how they play into the fighters game plans and how they would fare in the other organisation.
4. UFC just launched their sub thingy, no idea if it's worth it.