You do not need a licence to operate a recreational vessel for personal use (not for hire)
Insurance is case-sensitive- depends on what you buy, where you use it, and where you live.
Diesel: more expensive initial cost, heavier, and slightly more maintinence intensive....HOWEVER. Gas is louder, you have to run blowers to keep vapors out of the bilge (bottom of the boat), and they are not as fuel efficient.
Docking charges vary too greatly for me to comment. However, storing in the water means that you have to paint the bottom with special paint to keep marine growth and fiberglass blisters from ruining your boat. Most cuddy's are trailerable if you have a capable vehicle.
Most brands are pretty good. The only ones that I sometimes fear are Bayliners, and certain model year Chris Crafts.
Good luck
1986 Honda ATC 200 S
Some quads and a S x S
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Supporter of Uncle Rico's football camp. Since 1982.
If you are reading this in English, thank a U.S. Military VET. ΜΟΛΩΝ ΛΑΒΕ