A 'Speed National B' licence is what you are looking for, you can probably apply for one online, I just renewed mine online the other week and it popped through the door in 4 days, however for a first application I'd get it applied for sooner rather than later, before the rush.
You need to be a member of a car club, if you are not already a member I would pick Monklands Sportig Car Club or East Ayrshire Car Club, you will be asked for car club membership proof on the day.
You need a sticker showing how to switch the ignition off.
You need some yellow insulating tape wound all the way round the battery negative lead.
You will need a fireproof suit, and that can still be a cheap proban one (but just in case a nomex one would be recommended)
You will need an approved crash helmet, look for Snell 2005 approval as a minimum.
You don't need anything else, and if I were you I'd get the above and turn up and learn what your and your cars limits are before doing anything else
If you had some extra budget I would spend it on some fireproof driving gloves and some fireproof driving boots and a nomex balaclava, then a six point harness and only then toys for the car . . . it' all very well spending budget on the car but personal safety is probably more important
It's only 3 weeks to the first events in the season at the Kames sprint and then the Doune hillclimb, certainly achievable if you get the licence sorted out.
There are a number on here with some experience of sprints and hills, feel free to ask questions, but most importantly get the above sorted out and get some entries in and get driving, there is really no substitute for actually doing it
Some memories from last season from my year :
http://motorsport.ziplockk.com
I should be doing most of the events this year subject to work and all the other things that get in the way of fun . . . you'll meet a great group of folk at the events, very helpful and friendly, and that is as important as the driving in many ways
Fd