I've owned and worked on a Porsche 928S for 4 years (4.6L Front Engine V8, 50/50 weight distribution). I used it for a daily driver and took it to Auto-X events 3-4 times a month. The biggest thing on the German cars is definitely maintenance and parts cost. Availability is there, but I'd say 90% of your parts are coming in the mail.
If you keep the maintenance, those cars will give you back a lot of memorable miles. Forget about it if you're bringing it into a shop for work. The only time I ever went to a Porsche specific place was to have the water pump and timing belt done. I'm sure they'll gladly accept your paycheck though..you're almost better off finding a VW repair shop. All maintenance that I'm able to do with my tools, I've done myself. A cheap poorly maintained one will cost you more in parts/time/labor than buying one considerably more that's been kept in shape. And once you start working on one, you'll come to realize that Porsche (maybe all German) engineers have a non-conventional way of putting components together. Also, they have a way of cramming everything into tight spaces. Maybe this isn't as bad on a 924 since its a 4cyl, but the 928 was knuckle-busting galore.
Find the 924/944 forums/websites and join, you'll get all the help you'll need there including a checklist for buying used. Once you find the forum, check to see where everyone gets their OEM parts and what are usually the parts that go first on specific models. Check the prices... If you're still interested after seeing costs, and if it's a well maintained car as you say it is, for the price I'd say pull the trigger. That's a steal. But definitely check into 924 forums/sites so you know what you're getting into.
Keep it mostly stock, otherwise its even more of a money pit than the 919. But with that said, the best mods are definitely on suspension. Forget about getting more ponies unless you're pouring money into a charger. Koni adjustable shocks with Eibach springs paired along with the right bushings, sway bars, etc and some Bridgestone S03 and you'll feel like you're glued on the road. A borla exhaust would be a nice tone too.