Good to hear that you are going the software route and considering BFD! IMO there is nothing available in the form of a module that can even come close to software! I have been using BFD with my sound library, jazz & funk, for about a year now and through out that time, anything that I dream up becomes reality quickly. I also use Live and Reason for some things and everything works great.
Yes, BFD is a big program and the last two libraries are 55 gig each! I am sorry, but I am not up to speed on MACs yet. BFD will rewire into Abelton Live and you shouldn't have any issues there.
The big thing to look for in your setup is the combination of the computer, drives, and interface. (I would recommend that you get a very fast drive. At least 7200 rpm, just for the BFD data) Latency will be your top concern. There are a lot of topics on this covered at fxpansion.com under support.
We can keep this thread going here! I will help out as much as I can. The Mayor is a big MAC fan and he may be able to help.