Tom,

1) Start with a featherweight (12kg)
2) Go for a ram bot. This will allow you to understand the radio gear, the electronics, and the general principles of bot building.
3) As for the electronics, as long as you understand the difference between a parallel and a series circuit you should do ok!
4) ASK ASK ASK. There is a huge wealth of knowledge on this forum and you will save yourself a hell of a lot of hastle if you arent sure about something.
5) Most people have websites on their profiles detailing how they got started and the build etc afterwards. Read as many of these as you can.

Finally, welcome to the club and best of luck!