Figure out if you prefer a 2 stroke or a 4 stroke. Start lo look at all the different years and models. Watch Youtube videos, read forums, etc.
If you are a DIY kind of guy then you may want a 2 stroke. The newer models all have 4 stroke engines in them. I believe the last seadoo with a 2 stroke was the '06 GTI.
Also, unless you buy some of the smaller engine skis from the early-mid 90's, most will have plenty of power to do what you want.
As far as the hours go...that is a hard one to explain in just a few short words. A ski with very few hours that has sat for a long time can be much worse off than a ski with 200+ hours. It really all depends on the particular engine and how the ski has been cared for, so there is no "magic number" to shoot for with the hours.
If you look at any skis, you will want a compression test on the engine and if you intend to buy it you should test ride it. Ask the owner to provide as much maintenance info on the ski as they can, and then tell us what they said. Someone here can let you know if you are getting any BS.