The easiest way for you to accomplish question 1 is to set up each front door as it's own sub account. This way you can see which one generated the sale. Ccbill tech can set up all those sub accounts to share a common password file, thus giving every new member access to all areas. A bonus benefit of this; each front door can now have it's own members/index.html page, tailoring the experience to the member's personal preferences (ie: fav niche displayed most prominently).
Set your partner program to 'group', and you're in business. Each front door can be linked to as:
http://refer.ccbill.com/cgi-bin/clicks.cgi?CA=YYYYYY
&PA=XXXXXX&HTML=http://www.yourdomain.com/niche/index.html
(y=your account #, x equal's the partner's)