As far as I know there is no problem in the Class 2 medical with colour blindness. Unless you are aiming for gainful employment at the front of an airliner, I think it's a non-issue.
It is a wise move to get a CLass 2 either before you start PPL training or very soon after, in case there is some issue which will prevent you getting the licence. Even if there is, you may well still be OK for the lesser requirements of the NPPL.
Ask around for a good Air doc - prices vary considerably. Mine is very reasonable but he's in Gloucestershire - PM me if you want to know.
For self study, buy the books - I used the Pratt ones. Make sure you get the latest versions - the cheaper ones on Amazon may be old stock. Don't try to get the ground study out of the way before you start flying - you will need practical experience to marry with the theory.
Opinions vary about FS. I never really used one before I started flying, though I had loads of RC model flying experience which was (and remains) very valuable. Some people rate FS for Instrument rating training. My feeling is that for PPL training, FS would do no harm, but not much good. either.
Go and see more than one local flying school. You will be spending a good deal of money with them and it's important they make you feel comfortable. Don't pay them in advance. If they have a good deal on pre-paid hours which you really want, pay with a credit card.
Have fun! It's supposed to be fun!