Remember, motors are what costs you the most money, not the boats or trailers. I recommend you take it out one more time for a test ride and invite along a boat mechanic if possible. If that wont work then take it to a pro shop for inspection from a mechanic. Even if it costs you a few bucks now it may save you thousands later on.
From what you described it doesnt sound too serious. But unless you intend on changing out the cables yourself, that and a tune up will still cost you a few bucks. Check into it with a mechanic for shop prices before purchasing.
Health nuts are going to feel stupid someday, lying in hospitals dying of nothing.