As a fellow noob, can only share my experience:
1) There are no walkthroughs/guides
2) You will read and be told it's incredibly complex and difficult and time-consuming (which it is!)
3) Whether starting from scratch or not, there should be some pre-existing bridges (meshes) out there in different formats which you can load up to get a basic idea of dimensions/size. Rest is down to your modelling skills
4) Fed bridges are probably easier to do and more popular
5) err... that's it.
Hope been some use.
fellow beginner (WIP)