Here's my thoughts. Someone please correct me if I'm wrong!
Here's how I'd do it;
Motor speed control on auxiliary potentiometer controlled channels. You could use two seperate channels, but if my thinking is correct, you could actually get away with having both throttles on the one channel without any issue.
Buckets raised/lowered by pushing each stick up/down. Port bucket on the left stick, Starboard bucket on the.... you guessed it.
Steering by moving one of the sticks left/right. Which one you choose is up to you.
With the above control assignments, you could perform the various manoeuvres thusly; (The percentage values are arbitrary - just set as much throttle as you need to perform the manoevure, obviously you don't need to be at full throttle if you're only manoeuvring at slow speed)
For things like crabbing in a circle around a buoy, that is essentially the crabbing manouevre, but with slightly more/less bucket. With practice you should be able to perform all those manoeuvres with the above controls.
As for a suitable transmitter, you could use a Turnigy 9X, which comes with 3 potentiometers, you could use the two on the top if you were having seperate throttles, or the one on the front if you weren't (or I suppose you could use one of the top ones if it's easier to reach)