RE: need help
Bigtreds,
How much does the boat weigh? Are you wanting to run dry ground also?
Without knowing the above questions I would suggest a .46. If money is an issue, go with a Super Tiger. I personally prefer OS motors.
Servos. Use standard Futaba 3003 servos. These are standard size servos and will work well for your application.
For a throttle linkage, use 2-56 golden rod. The red with yellow core. You can get that from Tower Hobbies.
Glad to see you getting into airboats. Your gonna have a blast!! Let us know if there is anything else we can help you with.