First of all, try to find a M COupe that hasn't been driven to exinction heheh. If it is driven hard, check if it's properly maintained, signs would be brake upgrade, suspension upgrades, Oil change intervals.
Drivetrain from 98-00 M Coupe shares the same engine as the e36M3
Watch out for 98-00 transmission that doesn't pop back to the middle, I believe when you fist start the car in a very cold morning then put the car in 5th feather touch it back to neutral.. if the shifter stays on below 5th you may have a problem with the transmission clip (look at roadfly its very documented there). It is not a very serious problem but if your car is on warranty you can always ask the dealer to fix it for you. Otherwise, you can live with it by driving around for 10 mins let it all warm up and it will go back to normal. Its just very annoying because when you try to put it on 1st it goes to 3rd instead.
Drivetrain from 01-02 shares the same engine as e46M3
There is documented info on engines from 01-02 exploding look at roadfly, they sare the same problems as the 01-02 M3's
Trunk hatch mulfunction there is a easy fix for that
Some lights at the console doesn't illuminate, easy fix for that too by adding/replacing burnt light bulbs.
Key hole will freeze on -30to40!! You can't get in if you don't have the keyless entry.
Doesn't come with keyless entry!!!! Keyless entry cost around $600+
If your over 6~ feet you may not fit inside properly hehe
Seats doesn't drop low enough
Stock suspension is too high for my liking, there's a huge gap there
Watch out for cracked diff mount and cracked truck floor. THe Z3 shares the same diff mount as our fellow e30's. Due to that, with the M COupes higher powered engines the diffmount splits from the body. I suggest you read some info on roadfly about this because it affects almost all M Coupe specially older ones thats been driven hard. If there is crack BMW Canada might fix it or not, if not you have to get the plate kit from them, and then weld it.
After all I have said, I will still get the M Coupe. It's one hell of a car to drive and cruize around town heheh.