HI Edward
If you are thinking in terms of 2.4Ghz I suggest you take a look at
http://www.rcmodelreviews.com/spreadspectrumtests.shtml. This is an independent review of the various systems in common use. You should be aware that 2.4Ghz sets are almost always brand specific Ie you can anly use a Futaba Transmitter with a Futaba receiver. There are some after market receivers appearing that are compatible with the Futaba sets (GiantShark ex GiantCod sell) and I know that they do work but you need to be sure before you buy.
Binding is a once only process. Best done at home and once set should not need to be touched.
I agree that the T4U is readily available but it does not have the level of adjustment needed for the sail winches on the Cariad. Their Radio Link T6EAP at around the A£50 mark would meet you requirements much better. 😉
Your servos will work fine with any other receiver and they are no longer as manufacturer reliant as used to be the case in the 1970's. All modern servos/ESC's use a common female type plug. if your servos have the Futaba male plug from the 1970's they would need modification - and not just the plug. Good servos are freely available and full size start from about a fiver. I have bought from
http://www.servoshop.co.uk/ and they have a very large selection to choose from.
You will also find lots of other R/c gear including Futaba radio sets - make sure you scroll down the listings , they tend to have the expensive helicopter sets at the top!
You will find that almost all radio sets offered are mainly aimed at the aeromodeller and the settings often refer to model plane set ups. Don't be put off by this, they will work just as well on our model boats (with the exception of subs for 2.4Ghz).
The modes are again an aeroplane setting. Basically either mode1 or mode2. This is just an adjustment that allows for the throttle/Aileron to be on the right (mode1) or left (mode2) sticks. Not normally of great Importance to us model boaters but is Important if you want to use some advanced features on the electronic sets as some functions only work on specific sticks.
Apologies for the length of reply.
Have fun looking. 😀