1: I would guess a 6" vise would be normal, having a good 8" on hand for larger work is nice. I like having a matched pair (4"-6") for longer parts.
2: look at the fixed and movable jaw when clamping to see if they lift or tilt. (sometimes can be loose bolts under the fixed jaw or the centre screw on Kurt style vises being loose.) Snug up the centre screw and open and close it over the full range to feel if there is a worn/loose area. Looking for hammer marks on the handle can tell of abuse. There's probably more others can add.
3: Price is good to a little high for a 45 minute drive I guess, but that vise looks in good shape.
4: Is there a swivel base to go with it? Handle?
I like with the Kurt style vises that you can bolt the jaws on the outside of the fixed and movable jaws to hold large plates etc. It's nice for larger work, it might be heavy if you have to take it on and off a lot.
Darcy
Buying 2 matched vises is a really great idea for big parts!