Hello IanP. I don't consider myself a specialist in RC, but have some basic knowledge about the subject which might be of help to you.
First of all, the modern RC equipment work on 2,4 GHz frequency. The benefit of this is that the TX and RX are paired with each other and they do not disturb any other RC users near by.
What you need for your ship as minimum are a transmitter, receiver, electronic speed controller for the main motor, and servo to operate rudder. For more functions like lights, radar antennas, anchor winches etc. you can use your multi channel switch.
There are many nice modern TX & RX combos available at specialist shops or internet at very reasonable prices, like for instance this five channel radios:
https://hobbyking.com/en_us/turnigy...923&indexName=hbk_live_magento_en_us_products
Five channels are more than enough for controlling a ship, as a minimum you only need one channel for motor controller and one for rudder servo. Third channel could be used for your multi switch.
I suppose that your propeller motor is normal brushed DC motor with either 12 V or 7,4 V supply voltage. To control this you need an electronic speed controller (ESC), which is intended for brushed motor, has correct supply voltage, and has forward/reverse functions. So you need an ESC which is intended either for a car or ship. Not for aeroplane. For instance this:
https://hobbyking.com/en_us/hobbyki...605&indexName=hbk_live_magento_en_us_products
And last but not least, you need a suitable servo to control your rudder. There are numerous possibilities, you only need to select one which has enough torque to turn your rudder, but is not too big and powerful to do its work. Suitable ones are for instance here:
https://hobbyking.com/en_us/radio-servos/servos/best-sellers.html
For the additional functions like lights, winches, horns, etc you may use your multi channel switch unit which can be inserted into the third channel socket of your receiver, if the polarity of connectors is correct.
For further questions, please do not hesitate to ask more, I am always glad to be able to help.