Hi
Have done a lot of work with hobby ROVs.
The above advice is real good.
First stage :- is to get the two Arduinos talking to each other.(with the length of required umblicle cable)
Second stage :- Add a joystick or pots to the topside. And read with LCD.on bottomside.
Third stage :- add motor controllers. I used model boat/car ECCs to drive the motors (just use the simple Servo commands)
Bulge pumps might draw to much current for the L298.
If you need a two way information system get it working first.
Regards Antony