Hmmm, the very full train ...

Well, I would think that the train ride would limit you to Brompton/Merc, Birdy, or 16" Dahon. The Brompton/Merc has the smallest fold and a decent size wheelbase compared to the Dahon. For a thousand pounds, I believe you could get a Steve Parry version which would improve the performance considerably; although I have never ridden one myself. The Brompton/Merc has the smallest fold, can carry a lot of stuff, and can be rolled while folded.

Performance-wise, I think that the Birdy is a superior bike. You can get one with a Nexus-8 on the rear as well as several derailer options.

-G