Hi there and welcome to the forum!
Anyting pre 06 is before the facelift model so a few differences including non LED rear lights, rays not coming as standard etc. All this information is in the FAQ section in the forum.
There are ZEDS on here that have did over 100, 000 miles so as long as the car is and has been looked after don't see higher mileage being a huge problem. Personally I would stay away from any car that has been accident damaged.
As for issues, there are a few known issues that some peple have had including rear clicky axle, skipping BOSE system amonst others. Again, this information is all in the FAQ on the forum.
Good luck looking for your Z
Craig