For what you want to do, sounds like you need something in the 15 to 18 foot range. Look for a runabout with a V configuration. Stay away from the tri-hulls and boats built as ski-boats. Take that advice from a person with a tri-hull, it will kill your kidneys.
In fact, the greater the angle of V the better. Walk around inside of any boat your looking at testing the floor. If it has any soft spots, walk away. Make sure to check for soft spots around the seat bases or anything else that is bolted through the deck. Closed bow or bow rider is your prefrence. A bow rider is easy to dock and anchor while you are alone, but the closed bow is nice to keep things stowed out of the elements. If you find two or more boats that you like: Higher sides are better than lower sides, remember that you may need enough space to mount downriggers, fishfinders and the like, a canvas bimi is a huge plus for fishin in later months. As far as the motor goes, it will probably be older, so have a compression test done on it and change the impeller. And I almost forgot, get a galvanized trailer if at all possible. If it has to be a painted one, try for one built with chanels instead of tubes so it does not rust from the inside where you do not see it.