That is a very good question! I know culture towers stack.

I'm kinda new to the game, so I'd hate to lead you astray, but I want to say no, hangers and defenses do not cost maintenance. I'm actually kinda surprised the fighters/bombers in the hangers don't go against the pop cap though...

The thing with trading posts, is that early on, they suck. I've been playing with them and on my most populated planets, my income rate increases by +0.3 per trading post. Considering the investment on initial cost plus resources, plus log slots (upgrade # if needed)... it takes a long long time to make that investment back.

The problem with this game, is early on, resources/money is so tight, you have to really watch what you are doing. Then the game hits that mid point and it is the complete opposite, where no matter what you buy you will still have a crap load of resources. I'm still new, like I said, and I could be way off, but the game needs some fine tuning on "fees".

Instead of a flat rate on ship cap per tier, there should be a system like what was in Rise of Legends. If you spam a lot of ships, their cost increase per ship. As it is now, late game it is a steam roll, you have so much money and resources strategy really doesn't matter, it is just spam.

I digress (and babble sorry), I'm pondering starting up a game to see if trade posts do stack. I guess it would be cool if they did, but I don't think it would be worth the hassle if you are already tight on cash.