I think CJ is the only one here with the experience of twin engined airboats. His advice and comments so far are good.
I've flown twin powered aircraft before, but that's a different story.
But your gonna love the sound
Throttle control would be simple with dual servos and a 'y' harness, but like stated, would require manual adjustments. But the only way to do it unless you have more than a 2ch radio.
Props turning opposite directions would require one of the engines running a reverse crankshaft, which may or may not be available for that particular engine. In the airplane field, canting them towards or away from each other helps the torque issue.