Well I'm not sure, but I'll give it my best shot

1. No, the formations should be fine. I'm pretty sure about that one.
2. I believe that to cross a bridge or go through a gate they automatically form a column, so it shouldn't be a problem, you'll just get one long column
3. Not sure here, they won't get stuck I don't think, but they may be a bit more difficult for the player to maneuvre
4. There is a condition in preferences.txt called "Unlimited_men_on_battlefield" or something like that. I believe if you switch that to true, your reinforcements never get delayed. I'm afraid I don't know what the result would be. Try it