I've just done a basic connection diagram for 2 ch radios. Best to use a 2 stick radio 2 or 4 channel, with the throttle full throw and a ratchet, not a centering spring. Don't use a car radio with the steering wheel on it.
I see you are thinking of a 300mm boat, these are Footy's. Have a look at Hobbyking for 9 to 20g servos , these will be powerful enough for the sails and rudder for this size boat and cost about $5.00 each max.
Plenty of plans on line (Search Footy plans), quick and easy builds from thin balsa. Sails from a plastic shopping bag, mast 1/14" dowel.
There is a kit available from New Zealand based on a 1.5 liter plastic drink bottle. Search for bottle boat.

Welcome to the madness.

Kevin