1 - unless there's a receipt that shows that the timing belt has been
changed in the last couple years, I'd do that before much driving so
figure that cost in.
2 - not knowing where it came from be wary of floorpan rust. Seems like
405s rust from below, the opposite of 505.
3 - make sure the A/C runs ok, if not the firewwall connection to evap
needs o-rings and a recharge, figure that cost in.
4 - the heater door motor/ECU can be problematic. Be sure that the you can
control the temperature.
5 - check the tightness of the rear suspension bushings. Should be OK at
that mileage but at 8 years+, be sure.
6 - various dash switches may stick etc. Standard late 505/405 issue
7- check for evidence of water leaks (look under back seat)
8- does glovebox door latch OK?