Might I recommend the Spektrum DX 6 radio. It's 2.4ghz,computerized mixing. All trims, mixing, setting of throw lengths, and reversing of servos (if required after installing) is all programmable via the transmitter. Got mine for $199 dollars US currency.
As for the ESC's, using two of them through the throttle channel works great. My American Enterprise equipped with jet drives uses this set up, using a "Y" connector from the throttle channel Therefore, two esc's each controlling a motor, from one channel. Tamiya makes an esc that controls two motors also, as well as a company called Novak. That should solve your forward motors running at different speeds problem.
The available mixing functions of the radio should cover the steering challenges.
I realize the radio is intended for aircraft, but no one makes a surface frequency radio that suits our needs for boating purposes. The 2.4ghz radios are set up not to interfere with eachother, or any other radio frequencies, automatically, when you switch them on. I've had no problems with range, never had a loss of control, or have never been "mutinied" by someone elses transmitter taking over control of my boat. Best thing is, the reciever antennas are only two inches long!
http://www.hobby-lobby.com/spektrum-radios.htm?c1=google&source=camp16spekTamiya#40537 ESC TEU103BK twin motor
http://www.teamnovak.com/products/esc/1841rooster_crawler/index.htmlThe Novak unit is pricey, but it's also waterproof!
....Fair winds, and following seas,
Cap'n Jack