The Best bridge is a special one. Originally used in CoH1 for one of the single player missions where the player needed to blow it up.
I guess you took it because it looks great but that's all about the bridge. Unless not set to invulnerable i recommend to use it only in places where it cannot be destroyed or where destroying the bridge is of no concern. For setting it to invul follow this link.
I'd like to see the map because I don't think there is a limit that can be reached that easily. Even on large maps. There's a bigger chance you used bugged objects that cause the crashes.
PS: Did you check the stat graph (can be found under "advanced")?
Water is one thing but roads are just to complicated. Think of tracks or people using textures for splines in very creative ways - not only as roads.
I'd like to have a way to create maps without the need of using a grafics tool like ps or gimp but to make a mapgenerator it would mean to increase the work needed to create maps (markers for roads etc). In the end you would end up having less maps overall.
To be honest: I rather do not have a tactical map looking like the ones used by offical maps than having maps that are fun to play.
Edit: Correct me if i'm wrong but didn't the wb for coh1 have separate images showing at least the buildings?
I think my suggestion to make the fields smaller was misunderstood. I didn't mean to reduce the size of the fields to replace them with woods houses or whatever else. What I ment was replacing one field with two fields. Your map setup will remain the same, keeping the possibility of flankings while the reduced field sizes will need you to place more separators (bushes, roads, ditches, etc.) that won't necessarily break LoS.