All personal opinion. I'm bored.
1 sounds good.
2 you might want to go 18"s/19"s. 17"s just look too small on a 3 series. My friend ran 17"s before, and they weren't so great. He's running 19" CSL reps now, and they look great.
3 I'd think you'd probably be fine with KW V2's. Unfortunately, after totting around and taking a peek here and there, I've found that they only have V1 and V3 for xi (I think). About 2.1 grand from **********s, I've only ever heard good things about KW V3's.
4 Do a search on Cyba (Dvision autowerks), check out the tips he's selling. *Personally* I despise chrome. He has brushed aluminum tips, and also has anodized titanium ones, and I think they look great.
5 i'm looking at 45% front 35% rear. I have black interior, so I figured that's what's best for me.
Additional notes: Check out the M aero front lip and the Mtech rear bumpers. They look fantastic. I've seen both on friend's cars and they really set off the look of the car. Try not to chrome or rice, just go for a clean look. Get painted reflectors, that amber is freaking nasty.
In the end, just have fun with it.