btw, your generator is well made. Is there a write-up for the algorithms used?

As far as I remember, there were a couple of my comments on Reddit about how it works, I'll check it. There is also the source code of some early version of the generator on GitHub.

Also, the rivers usually have 1-2 bridges. There should be more along a long river, I think.

Rivers in MFCG are pretty large, usually around 50-100 meters wide. In Middle Ages it was expensive to build a bridge over a river this wide (and probably still is nowadays). I would argue that 1-2 bridges is a reasonable number (augmented by ferries), although it could vary depending on many factors (size of the city, its prosperity level and strategic position, available materials etc). But actually I don't define the number of bridges explicitly, they are just points of intersection of large roads and the river. In some cases a single "secondary bridge" is added when it looks like there are not enough "primary" ones.