No worries, personally the brakes should be the first thing to sort out, yes the brembo's are good but some decent pads and maybe braided lines make a massive difference. Discs less so unless you throw the car round a track really i guess.
You don't need to do everything at once at all, only thing i would say is wait for the remap at least until breathing and exhaust mods are complete or you will have to go back for tweaks.
A throttle controller is ok until you get a remap, it gives you a more instant reaction to the pedals, a remap does this along with a lot more but not as cheap....
Decats = MOT fail, HFC's are less harsh and MOT safe
Feel free to PM me, always happy to help, I am no expert by a long way but I know what I like and others seem to like it too