if you can get the fit included, why not. you know where not to go, but since Titleist for one one are charging £40 for a fitting - not recoverable - your options may be limited.
Dont get custom fitted, you said yourself you could grow another foot, so whats the point?
By the looks of it you already have a pretty good set of clubs, so stick with them, learn the game, improve and get custom fit in a few years time when it will be more worthwhile.
In the meantime, if your parents want to encourage you with your golf, how about cash for handicap reductions to add to your exam cashpot?
Get the grades in the bags first and then chill. You're lucky and have your golfing career ahead of you. Personally I'd wait for C/F and the time you've found beer and women there'll be loads to chuck your money on apart from clubs. If you can resist the lure of sex and hangovers and stick with golf or come back to it in due course that'll be the time to get a fitting. You'd have stopped growing fully and will have some cash on the hip to get a good set of the Ping I24's or R48's
I learnt to play with my dads old hand me downs and I think there is a lot to be said for learning to play with clubs that are too heavy for you...
My advice would be to play with the clubs youve got now and just practice knocking the cover off the ball, you can learn to find it later. I reckon its a lot easier to develop power at a young age than it is when youre older.
Dont know what you should do with the money tbh....