The Mill Road queue starts outside the Away end at full time. Stay inside for a beer for half an hour and the queue reduces
No one will check for a ticket at Lewes so you’ll be fine
The Park and Ride scheme runs from Mill Road - just as you enter Brighton off the A23. (Get there before 12.45 or it will be full).
Or you can park in Brighton and train it in (expensive option).
I have never yet had my ticket checked either on the train or at the Park and Ride stops in...