OK, a Standard Gauge train around the cake on a 60" diameter table isn't so crazy if bride and groom are into it. And you don't want to go overboard with a bunch of other train-theme stuff, that sounds sensible to me. The cake could be somewhat elevated above the track level, you don't want it integral with the cake. Don't want sliced cake getting dropped on the train so you want a sober server with a steady hand. An engineer should be appointed to oversee the railroad operations and prevent derailments.
The train could have gondola cars with the cutlery and candy favors, to give it some function. Yeah, go for it.
Maybe someone will give you a Marx honeymoon express for a wedding gift ...
