I have a Big Swamp Buggy,cost was a factor so I went with a O.S. 40 LA remote needle ,and 10x6 prop its pretty fast.
You should have enough room to swing a 11" prop inside the prop guard, I wouldn't run without it,if you do be real careful of sticks hanging over the water,and these run ok on ice and hard packed or glazed snow,if you run on land definitely run the prop guard it will save alot on damage to shrubs.....
I'm running Futaba FM radio.
Make sure to tighten up verticle clearance on rudders, when the engine is running they bounce up and down creating noise that can interfere with radio,I used some plastic washers to take up clearance and plastic pushrod too on rudder,but a metal cable on throttle.
Anything else I can help on let me know,these Swamp Buggies are probably the most fun per dollar that you can get in RC.
The pushrod and cable are both Sullivan Products available from Tower Hobbies.I used the cable on throttle because you can't bend a plastic pushrod into a tight enough curve.
Fuel intself is 5 percent nitro also available from Tower,you should use what the maker recomends,lower nitro is cheaper and easier to tune needle.
later Mad Max