Glen,
As regards model cars, if you buy a kit by any of the manufacturers, the instructions are usually sufficient to get it built - setting it up is what takes the real skill. that's what comes with experience and being part of a regular club - if it's more car information you need search out BRCA - they are the main organising body for model car racing in the UK - and should have links to relevant sites and club info.
Yes , you can use your radio set in either a boat or car
Before you commit to buying anything expensive - visit your nearest club and ask questions - see what they're all racing and go with the majority.
I used to race a Grasshopper , hence the 'handle' - and with it I have beaten quite a few of the better cars of the time.....by heck, that was nearly twenty years ago...