First of all, love the game.

However, one of the most annoying thing about it is when I have many planets, I have difficulty finding the best place to build some structure, typically a research station. That's because I have no idea where I have the free place on mine 10+ planets.

Here is what I think can be done:

When you mouse over the structure (or ship or planet upgrade) in the build menu (bottom right of the screen), even if it is grayed out, then all planets on the map, where this thing can be built should light up. This will be especially useful when you are in that zoomed out view - you will see all planets at once where you can build the station (or ship, or make a planet upgrade)

If you at the same time press some key (for example alt) and hover over the same icon then instead of lighting up the planet where this thing can be built, those planets should light up where the structure is already build. This is especially important for finding those ships, like colony or scout. Just mouse over build menu with alt pressed and you see the planets where you have those ships!!!

I do not know about you, but this single thing will improve my game experience a lot! I think it is a must have!!!