I like the GUI of AoW:SM. It's very clear and the idea of unit-characteristics on the side is very useful (especially if you have a 16:10-screen). Icons are not the best, because you don't understand them if there are many types of it. So the text in AoW:SM is a good solution too.
For citys is the GUI of AoW:SM very good too: in the middle the city, left the menu to build units and buildings and right more information.
Please do not something like overall icons with infos, chats and so on. I want to spell mass confusion on the enemy-army not on my brain 
For an continous turn based game its important to see fast the enemy-characteristics to give the correct commands. With magic against an enemy that have magic immunity is not the best move. I hope your GUI will be so good as in AoW:SM 