You'll want to get a different charger if you go with the 3300 nimh batts. You could probably use that charger if you wanted to babysit them with a temp gun and shut them off when the batts heat up to 110-120* F.
I'd leave the 4wd connected. With good batts and a clean motor you should still get a good runtime out of your batts. 5 minutes would be decent even though it'll probably go longer before the batt dies. But the longer you go the more you strain your batts and motor.
I'm sure there's some more qualified elec guys who can give you some better answers. I'm more of a nitro guy myself. But just thought I'd throw in my opinion.