Each major model RR publisher, Kalmbach and Carstens, has a book on bridges. I think there's an info packet or whatever they're calling it on bridges & trestles (probably just a shorter version of their book) available for download from the Model Railroader site. And, if you can find the back issues, I know there was a series in MR (and probably one in RMC as well...there have been a couple articles lately) on bridges & trestles.
I think the photocopy idea is great! Try using colored pencils to 'weather' the rivets a lighter shade and perhaps even add a small amount of rust...although your section foreman won't be too happy.
Central Valley makes a bridge tie strip that's really easy to use and would work well on top of the girders. I'm no mechanical engineer, but I'd say over water that swift if you had any piles or trestle bents, wood or steel, they'd need good solid footings with a wedge shaped breakwater on the upstream side. A girder or other steel suspension type bridge would seem the most logical to me.
Glad someone mentioned John Allen...yep, he'd have hand-carved (or drawn) stone arches on one, a timber through-truss on another, and girders on another, or any combination. A balasted deck girder makes the most sense for the area with the turnout, but I've seen photos of wood decks with turnouts on them.
Galen