Since you mentioned size is a factor, keep in mind that most non kit lens adapters push the lens out. For ltm/M lens, and probably Pen lens, the distance isn't much, less than 1/2" or so, but with SLR lens, the adapters get quite deep, probably over an inch.
I think Pen lenses are probably ideal, since they were designed for about the same size image circle and like ltm/m lens, the adapters can be relatively short. But watch out for yellowing/browning in some of them, can probably be cleaned, but not sure.
Virtually all SLR lenses can be adapted, but it makes the kit a lot bigger with the needed adapter.
I'd recommend to try a NEX first, it does take getting used to not having a low eyepoint VF and while I've adjusted, I can certainly understand how many folks can't or haven't adjusted.
The IQ is great, better than my D40x and M8 (except for IR), and with the latest firmware, the menus are fine. It's the lack of VF that is a like/hate type of situation with many folks.