Re: Trailer Brakes
1. Electric brakes are better from a driving standpoint as the other posters have pointed out. The trick is needing to get ones that can be immersed. Hydraulic brakes would be fine on your relatively lightweight trailer provided that you have a reasonably good tow vehicle. What are you using? One thing about hydraulic surge brakes is that they make it really hard to back a trailer up a hill so make sure that your parking space for your boat doesn't require this. Obviously, going down a boat ramp is just fine.
2. I don't know about bringing it to your auto mechanic but many trailer places can handle this type of install. I actually used to tow a trailer a lot that was built by the local trailer place.
3. You can absolutely do this yourself provided that your axle has the mounting brackets. If not, you need to weld some on or swap axles. Probably the easiest thing to do would be to bring it to a local welder. Give yourself plenty of time, the install is not that hard but you always seem to hit a hangup such as a frozen bolt.