I am probably gonna buy this script because it sounds great. I just have to wait until my next payment on my paypall account, because i just started using paypall and do not have mush on it.
1. Yes, that's the way this script works. If you add more than one domain on signup page, users can select which one to use, like username.domain1.com or username.domain2.com
2. You can apply almost any phpBB mod to it, but be aware that if you want to add a mod that requires changes in template files and you have loads of templates installed (usually hosts have all possible templates installed so their users have larger choice), it will be a nightmare to edit all templates.