CUA implementation in Solution Manager

We are installing solution manager here for the first time. I see other postings of using Central User Administration(CUA) in Solution Manager.

The questions I have are:

1. Is Solution Manager just another R/3 instance?

2. Can you setup CUA in Solution Manager and centrally manage all R/3, BW and APO users/instances from Solution Manager?

3. Are there any special considerations for setting up CUA in Solution Manager as opposed to a QA instance of R/3?

Any advice would be greatly appreciated.