yes, yes, and yes. You can map windows groups to ACs groups. The gotchas are:
You cannot use nested groups in AD (e.g. testgroup contains testgroup1 and testgroup2).
A user can not map to multiple ACS groups. For this reason, as you mentioned, you want the most important groups first. For example, if you want admins to map to admins and users to map to users, you should define the admins mapping above the users mapping (assuming all admins are users).
-Eric
