PF
Didnt do Cranwell but did one of the other millitary colleges. In answer to your question about fitness, just do some training to build up your stamina. Some running would be a good idea . Do soom fast walking in boots aswell just to get the feet used to wearing them. Increasing your stamina will not only make the phys easier but increase energy levels when you (inevitably) get knackered doing all the other stuff (long days studying plus physical stuff).
Good luck
TS
PS Don't worry about the flying training too much, just enjoy it whilst you are doing it. JEFTS isn't too bad!!