Hope you got a good deal from your dad, you have a long laundry list of thing to do!
Turbo, when active should read above the 5 mark. Any less and it won't go like it could. Pull the hose feeding fresh air into the turbo. Try and push/pull the vane inside. If it moves, the turbo is heading out, needing replacement or a rebuild. At 162k miles, I'm betting you need turbo work.
Gear shifting issues is probably the shifter bushing issue, again, at 162k probably all 6 need replacing. search this site for info on part numbers and instructions. Tight shifting is SO much nicer...
There are plastic/nylon parts that actuate the heater that break. Roosport sometimes stocks replacements made of metal, give them a buzz on where to look and if they have the part in stock.
The horn and cruise both share the same fuse, and both have to have the clockspring in the steering wheel functioning. Clockspring is just that, a spring that keeps the horn buttons and cruise control connected to everything they should, even when the wheel turns. Separately, the horn relay under the hood rusts out easily, and there is a switch the the clutch has to activate, problem being a hole in the plate in the clutch pedal needs to be plugged to make the switch work.
That's all I know, have fun with that xr2...