Lots of potential problems on any 2 stroke that old: carbs, oil injection system, compression, etc..........just imagine someone wants to sell you their 16 year old leaf blower. Before you buy any used 2 stroke do a compression check and a test ride.......that is the only way to insure the engine and pump system are OK. If the compression is good, and the engine starts cold, reaches maximum rpms, doesn't smoke excessively, doesn't bog in turns, doesn't have excessive corrosion, etc., then you might have an OK ski. If you skip these steps plan to join the "I just bought this ski and now it won't run" list on this forum............there are a million posts just like that.
Maintenance requirements: check oil lines, flush ski if ridden in salt water, clean/rebuild carbs periodically, rebuild top end, etc..
Great choice. The 95 should be WaveVenture the 98 is the new version of the WaveVenture the XL. Are these the 2 or 3 cylinder versions? Personally I prefer the more powerful 1100/1200 3 cylinder models. Do what Ernest said so you won't spend your summer rebuilding engines but rather riding.