Hi,
Welcome to the madhouse, you will get lots of advice some of which might be helpful - or not!
Anyway, where to start. Check out the rating of the motor and buy a new battery matched to the voltage rating, use Nimh batteries for this, they are cheaper and easier to charge than Lipo, also the weight is useful for a little ballast.
If you are electrically minded in anyway, try and find out what the current draw on the motor is with the hull in water, this will allow you to get a speed controller to suit.
The controller in the boat is an older resistance type controller, it will do the job ok (as long as it is undamaged), but, it will waste power and reduce endurance. You should consider an electronic esc.
This guy is very helpful and has good products:
http://www.action-electronics.co.uk/The radio gear: for boats you need either 27mhz, 40mhz or 2.4 Ghz sets. That one of yours looks like 27mHz. If its still working, there is no real need to change it, just put in some new batteries and make sure the crystals in the handset and receiver match.
Once all is powered up, check operation of the steering servo, it may be ok, they are quite robust. If not, replacement with a standard servo is cheap enough.
Having done that, test in the domestic test tank and if all ok, off to the pond and have fun.
Hope this helps, keep us informed and, we like pictures!
Ian
