You should maybe lookout for a Town & Country. Same platform, more room, 6 way passenger power seat instead of the 2 way in a Pacifica. Pacifica is literally a chop town minivan. I know people who have them and like them, but to me they have no advantage at all over the higher roof version and do have a lot less room and utility.
Drive it. Feel and listen for unusual vibration, pull or noises.
Look it over and under.
Ask for maintainence records or proofs.
3.5L should have t/belt and w/pump at 100K miles. Make sure that Everything works.
A clean, well-maintained vehicle usually means that they cared about it.