As far as where to put your $100, I would put it on PS because I think their rake might be kinder at the micros and you get their first time $50 bonus (if you haven't already)...

Then, if you make $600, you could switch over to FTP and take advantage of their bigger bonus.

I think 20 BI will be okay to start with, as long as you are willing to drop down pretty quick if you lose.

Good luck.