Mark, Sorry if this thought is a "repeat", but as your plan for the lower level girder deck bridges evolves, make sure the pilot of whatever locomotives you plan to run will clear the deck bridge as it enters from a curve.... It appears, from the photos, that at least at one side you have a switch located right at the entrance to the bridge. I didn't read every post above in super detail, but you might consider making it the type of bridge where the "girder deck" is under the tracks, so you have unlimited swing room entering and leaving the hinge up bridge section. The other benefit of below the track deck bridge is it could hide some of the wood side frame, the drawback is you'll feel like there is no protection from having a horrible wreck there where something could go to the floor.... My suggestion if that is a "concern" is you could put up clear plexiglass sides to prevent drops to the floor.
I thought I had enough swing room on my Atlas Double Track Truss bridge with an Ross Regular 0100 switch, until I unpacked and ran my B&O EM-1, needless to say, had to move the switch away from the bridge about 4 inches, as the bridge wasn't going anywhere.
