Not sure everything got answered, but I'll try.
#1 with the Sound Devices 702/722 or the Marantz pmd660/pmd671 is there not a need for an a/d anymore? (I.e. can I go Mics > Pre > device and not have to worry about the A/D?) [Side note: Yes I know that the 702/722 has an internal pre]
I'm not as familiar with the Marantz units (not owning one), but I'll assume the others are right. Simple answer is that these units have very good pre-amp A/D units, and most people that run them seem to just run the mics right into them. However, as with everything, there are some people that prefer to front them with an outboard A/D, such as a V2 or V3.
#2 If the above is correct, is there really a difference between the A/D on the 702/722 and the Marantz recorders??
I believe they are both highly regarded. Without starting a flame war, I think the Sound Devices A/D and pre-amp are considered pretty pristine, while it seems some people complain the Marantz pre-amp is a bit noisy. This can be fixed, though.
#3 On the 702/722 How long can I expect the battery to last if I am running it with the internal pre?
Short answer: hours. The 702/722 use camcorder batteries, and depending on the size, you can get many, many hours out of them. More importantly, since they are so small, it's easy to carry several spares, and swapping them out only takes a few seconds. I could probably record for the better part of a day on three good sized batteries (I'd probably run out of storage first).
#4 How much does a used Mp2, V2, and V3 Run these days?
No idea. I'd suggest checking the Yard Sale for the most accurate, up to date information.
#5 How do you power the 702/722 and the Marantz?
Marantz runs on 4 AA's; 702/722 on camcorder batteries. The usual methods to extend time apply, but again, it seems pointless for the 702/722 given the ease of swapping batteries.