I doubt there's a helicopter book I haven't got and read so .... hhmmmm... Norman Bailey .... I found them very dry and, to be honest, a tad advanced for PPL level.
For general reading, I recommend Randall Padfield, Learning to Fly Helicopters. I read it even before I started flying. It's readable and informative. For principles of Flight, you'll want Wagtendonk's book. Other PPL stuff is the same a fixed wing so either go for the Trevor Thom series or Jeremy Pratt.
Later on, you may want to invest in Cyclic and Collective by Shawn Coyle (he's a regular poster on Rotorheads) and anything by Phil Croucher.
You can do the exams any time and there's no age restriction but you must complete your PPL within 18 months of passing the first exam so be careful with your timing - you must set out a rough plan of timescales. You will also need to have passed all the theory exams before your skills test. There is also the Radio licence exam and practical test.
I would also recommend you learn to love LASORS - goo-goo it and download the latest. This will explain all the legalese you need. It's dull and sometimes hard to interpret but you might as well get to know where the stuff is if you're going commercial!!!
As for medical ... I would advise going for the Class 1 straight away. If there is any reason you that you fail, you may still get a Class 2 for private flying but you need to know before you invest too much and money. Once you have the initial class 1, you can let it lapse into a Class 2 and only renew it when you're ready for the commercial flying (I believe the limit is five years).
Your budget is a little optimistic!! You need to get an hourly rate quote from a couple of schools and make sure they give you the VAT inclusive rate and also the landing fee charge (usually per hour for helicopters). The skills test and licence fees are astronomical and may be more than £500 together. Also, some schools charge for each PPL written exam (others don't). Allow for equipment (Transair, Flightstore, Pooleys online); kneeboard, charts, flight navigator (get a CRP-5 now if you want commercial). All these little costs mount up so be careful.
No worries about asking!
Cheers
Whirls