My Z is also my weekend ride, it's a '10, had it since December and have about 6k on it.
Ya, If you are not exactly sure about the color then wait! Make sure you get what you want the first time.
Private party > dealer: If you are financing, get pre approved with a credit union or what not, find the car you want then let your lender know. If the guy owns it outright your lender will draft him a check, if he has it financed your lender will draft a check to his lender. Either way, you drive home with the ride.
As for DMV, your lender will typically take care of that for you. Otherwise, DMV is very simple to deal with. Maybe a VIN inspection, they basically come out and look at your ride. Say looks good.
I've bought more than one car per year since 2006, I know a little
.
one more thing I wanted to add. I would buy a single owner car any day hands down over anything sitting on a dealers lot being sold as "used".