as far as interior do what raptor said..also grab some seat covers if its that bad
As for the A/c..depends on whats wrong...the expansion valves are known to go out on our cars..test for leaks also.
or do what i did on take your compressor, lines, condensor, and everything else..who needs that anyway
and for the major checking besides looking for oil leaks, boost leaks, and smoke from the exhaust thats all i can think of right now..check the belts..all the lights..basic stuff
also if you do get it i'd invest in a valve cover bolt set from twosrus.com if he still has the phillips head bolts on there..
since torque is limited on them the valve cover tends to leak
and the hardtop is more of rarity within the mr2 family
has a ton less of body flex.