Once or twice a year, somebody appears and says women should wear more clothes, then they vanish quickly. (Shills for big textile industries?) Gotta give it to @NotReallyHelpingHands, they're more persistent then the usual troll.
Possible, that'd be something to have an AI look into if you want this implemented. Also note that for a bridge, pathfinding isn't really needed, so just to have the units "walk" across the bridge should be easy.
Not really.
That's a bit difficult, I've done it before tho:
A: make the "bridge" a unit
B: give it Build Restrictions like a regular building
C: give it a unique "amphibious" passability class in passability.js
D: work out any small details like cost and foundation and stuff.