Had a quick run around of your map and found a few things.
1. The map is quite small, but despite this, I found it really easy to get lost, you should really put in some more signs
2. There needs to be more ways to get up, especially up to the very top, otherwise once one team gets to the little tunnel, I'm guessing it would be next to impossible to try and stop them.
3. Some of the side paths are very far out of the way and quite hard to find
4. in payload races, it's probably better to have the enemy cross close to your base towards the end, not right at the start
5. It's quite a long way until the carts meet, maybe push them up a bit
6. Some of the stairs are a bit thin, maybe make them a bit wider and put railings on them
7. I think you should be thinking about optimisation very soon before getting to much further into the map. Almost the entire map is rendered when the player is on the tower, and add fighting and the like and some of the older systems probably won't cope with the map fully detailed
Otherwise, I like where this map is going, just a few small things to fix/think about, I only ran around by myself so I have no idea about how it will play out, I'm guessing very close fighting and the possibility of a very quick runaway with no chance to catch them, otherwise, I'd enjoy to play this soon.