Have a look at a
system chart to answer 1 and 2. If you want to use the reducer or flattener you'll need the CAA to get focus. Some of the adapters would have come with the scope. It's an M52 thread on the back of the flattener. I got an M52->M42 adapter off ebay for about $5 to attach it to my wheel.
Dunno about the clamshell, I got my fs60 in rings.