1) I don't know this one
2) I've had no problems with the Exage stuff that's passed through my possession. I wouldn't hesitate to use it. I'm sure it's very serviceable for the typical service I think you'd need.
3) Yup, it should thread on fine. Depending on your dropouts and spacing maybe you'll need an axle spacer to get some room between the small cog and the dropouts, but I really doubt it.
4) They should work and I read a lot about certain pulls being for certain brakes. I've mixed and matched all sorts of stuff and I'm not an expert in pull ratios etc. If it pulls and stops, done. I imagine you should be fine.
5) I only have experience with Claris 8 speed and Sora 8 speed, so I'm not sure what's best here.
6) I love BioPace and make no effort to remove it when I get a bike with it. I bounce in my saddle less at higher cadences with it. My first fixie was BioPace for about 2 years, because Sheldon said it was okay. You'll find people on both sides of the fence. A variety of non rounds chain rings are popular again. It's up to you.