To answer the lens question, SSM is the Sony version of a fast, silent motor built into the lens, which is used instead of the screw drive system for focussing.
In general it is a significant improvement over the older screw drive system, though some people have said that it is not as fast as the screw drive on a few older top end lenses.
Sony also have SAM, which is a cheaper in-lens motor system.
Sigma HSM and Tamrom USD lenses have a similar system to SSM.
Which body? I have the A700, and it's a great camera to use - given a choice I'd upgrade to an A900 as it's even nicer - but that is a personal preference for FF OVF over crop EVF
If I had to buy new on a budget I'd certainly get the A65 over the A55 - the EVF is incredible on it.
I wouldn't worry about the size of the files - external storage is cheap, so you can always archive older images away once you have processed the ones you like, and the level of detail an options for cropping that the 24Mb files give is great (based on using an A900 for a day).