Grounds need to be ;looked at cleaned re done. Re solder the DME
Belts hoses rad water pump will all be needed if not done recently
Bearings in the impeller shaft can go just get a rebuild from George at 944 ecology
Plan on an accusump or some other supplemental oiling as the rod bearings are a maintenance item and when tracked they can fail quickly as the oil runs up the Sid of the pan (twars the passenger side) and the motor starves for oil. This is mainly due to the motor being set at a angle (about 35 deg or so)
Ball joints in the newer cars don't like huge tires and lowered suspensions. The older steel A Armed cars and the early 924s (1987) seem to not mind this as much.
To get it into autocross shape plan on.
Dealing with the oiling problem accusump is the best way for little $$$. Cross Drilled cranks and what not are another rout but the $$$$ starts getting nuts.
Koni shocks, Koni Struts (yellow sports) Don't cheep out here.
Weltmeister bars front and rear. There are other options here but this is a sure winner and completely adjustable.
Iboc front springs (lowering the car about 1 1/2 inches stiffened it up a bit with the progressive rate)
You can put weltmeister torsion bars in the rear but this is a real pain to get set up correctly. If you are thinking of this go to a coil over set up (trust me on this) More $$ in the short run but up and working in a couple hours instead of many many hours of work to get new bars set up.
Porterfield pads (or Hawk's) seem to work well. You can spend a lot of $$$ on upgrades to the brakes to an s or 951 spec and some swear that it is an important upgrade. I have had the stock brakes in my 924s with the better pads and never had a problem. I am not saying not to make this swap but I have not seen a need yet. If I was just starting out (when I used alot of brakes this could have been important) I now use alot less brakes so this is not that critical in my book but still nice to know it is there if you want that little bit more sense of security I guess.
If you get an older car (pre 85.5) plan on swapping the tachometer and the speedo around to put the tachometer in the center.
Remove the rear seats as they are useless anyway. Now you can install a bar. some real seats and 5 points.
These are the major mods that really improve the car.The list little things goes on from there.
They are great cars!!! I love my 924s it is a blast on track or killing cones. I really dont remember what a stock one drives like. I think I would be disappointed.