Okay.
At a minimum assuming you want full house control of all control surfaces, you will require the following.
Four standard sized servos.
One ESC (electronic speed controller) I recommend 20A continuous current rating or higher.
A decent receiver with 6 channels or more.
A BEC (battery eliminator circuit) to power the radio equipment. This is often built into the ESC, but some are better than others, and with four servos hooked up, you may want a separate unit, especially if you're running a system voltage above 8 or 9 volts.
You may need some form of switcher for the ballast system, but that does depend greatly on the type of system you have built. The standard Sheerline system uses nothing more exotic than a servo and microswitch.
Motors are subject to performance requirments, prop size, pitch etc. However I would aim for a shaft speed of about 3500-4500RPM.
A good sized battery pack. System voltage is upto you, but nothing less than 6 volts, and most model submariners with boats that size run 12 volt systems.