Only you can truely decide what is good.
From looking at you sketch, it looks like it is going to be an "alamo" type map. While this is a very realistic style map and lends itself for fun playability, it is bad for frame rate. Read the tutorial on hinting:
viewtopic.php?t=1458Basically, you want a tall building in the center of your map that touches the skybox. As you notice in alamo, there isnt any part of the map that touches the skybox. The place where you get the best frame rate is inside the fort walls, but this is not where the action is.
I also recomend mapping in sections. create a general "block map" where you outline all the builds and sctructures (walls, rocks, tunnels, etc) that way you get the size ratios right from the start.