Turbo car help

[Eclipse4ever]

I have decided to buy an 1997 eclipse GSX. It will be about 1-2 weeks before I get the car due to waiting for paperwork and registration problems from previous accident. So far I know the car needs battery, timing belt,iol change,one pulley needs change,spark plugs. The car backfired once while I drove it, but i think if I change the spark plugs and wires it might fix the problem. Also the differential is leaking very very little. I am thinking of changing the differential gaskets so it would stop the leak however I dont know how awd are, why would it leak ?
Also the RPM's play little up and down but I think after maintance it would fix it. A couple of days from now I am going to do a compression test on the car. Can you turbo guys give me some things I should be looking for ? Engine sounds noisy but every one I ask tell that its normal ( maybe I am being paranoid from all the crankwalk). Can looks good and engine is stock except big 16G and Apexi exhaust. What should I check on the turbo car ? Any suggestions ?