Brighton Marathon Logistics.
PG2. seems like a workable plan to me. Withdean park and ride is easy to get to from Burgess Hill. Just before you hit the Brighton traffic which can be bad on a Saturday morning.
Agree about the great shopping. Plenty of good resturants to choose from as well.
Brighton's a bit bigger than Banbury so don't get lost. the locals are friendly. esp if you are wearing lycra.