It is looking good! Some nice textures you have there.

Small suggestions: The little green hexagons on the north wall look a little too 'clean' (they're unshadowed as well). Not sure what you're using to make the map but it might be worth putting a drop shadow / inner shadow so they integrate better with the wall. Some of the elements have a black outline and others don't (e.g. the wall and the hexagons) which lessens the effect of an integrated whole.

Not sure if the ship on the left is meant to be in the air or on the ground - you can suggest either by using a drop shadow and playing with the distance it is away from the ship.

For rules at battles on this scale you might want to take a look at 'At Close Quarters' by BITS which is for Traveller but could easily be repurposed for your needs.