Well, the timer can be reduced. I set it to 25 minutes to give both sides enough time to prepare, but of course it can be reduced if it's too much time. However, a little time is required, just for when playing with the AI, which would definitely crush the invaders in few minutes if starting with 50000 resources and with the opportunity to open the gate
The trebuchets don't have long range. Those on the third level can't hit enemies in front of the gate^^
(Also, they're not equipped with fire stones from the beginning, that's just a visual effect present in the mod. They can be upgraded, though, and trust me when I say they're their only defense if the attackers arrive with a lot of bomb ships. Also, if destroyed they can't be rebuilt^^)
For the shores I don't know. Considering that I started from the original map, that was the original size of them. Maybe I can try lowering the water depth, but in that case I don't know how ships will look surfing on it (I don't know even what is the minimum depth required to make the water unpassable for troops and passable for ships, considering that right now the water depth is set at 80)
But don't worry, attackers have a lot of advantages to take over the defenders, which includes outposts, settlements, and especially Bomb Ships^^