Hi Mike
1: Don't use 165 - it is an old release, you can download the latest m257 from the download section of CATVX. For 8 inputs, you will need the LFG4 card from Active Silicon. The inputs are composite. For 2 or 4 SDI or HDSDI inputs, you will need cards from their Phoenix range.
2: The latency on the Active Silicon cards is very low - I am not sure exactly how many frames - maybe someone else has these figures?
3: Yes you can use Dual and TripleHead2Go's, there is a mix setup which allows edge blending with variable overlap.
if you need more info, please feel free to email or PM me.
regards
Nev.