I'm no mechanic but here are a couple of tips....
Hopefully the previous owner either had fuel stabilizer in the gas or ran it dry before storing. If you had any old fuel in the carbs that sat that long, it could certainly cause a problem. You can buy a can of engine tuner at a marine shop (not auto carb cleaner) and run it through or you can buy a product called Seafoam at most marine/automotive shops which will help to clean things out. Still, if you have too much gunk build up in the carbs from old gas, those things might not help and you may have to rebuild them.
Another thing I would be concerned about is the water pump. A water pump has a rubber impeller in which the blades remain in a bent position. If they have not moved in a few years and have been sitting out in the elements, I would recommend changing it. (Even if that was done before the owner put it up.) I believe the motor manufacturers recommend changing them every year or two anyway.
I would check the condition of any fuel hoses and even look for signs of any critters that may have taken residence in the boat or motor. (chewed wires, nests, etc.) Check that shift, throttle, and steering cables operate freely. Check spark plug condition and gap. Make sure that the tanks are completely empty before refilling them. Even if they are empty, I would make sure there isn't any dried up gunk or rust in them. If this boat uses portable tanks and there is any question, I would replace them. The 6 gallon tanks are not very expensive but not sure what your rig uses.
That's a start....I'm sure others will chime in on some suggestions. Good Luck and remember...
B = Break
O = Out
A = Another
T = Thousand
And
A boat is a hole in the water into which you throw money.
If you understand this, you will have no problems being a boat owner.
Good Luck!