I think check in for ferry closes at 21:30. Trains are modern Thameslink 12 carriage, with horizontal bike storage in carriages 3 and 10. But plenty of space in other carriages. As above, train to Brighton. There’s a below cliff promenade you can cycle along as far as Saltdean, then cycle path on right up hill to Peacehaven, then drop down to Newhaven and across to pub.