Interesting game, I like galaxy management games like these. The problem here that too little information is given to the player, for these kinds of games it's always nice to have as many numbers as possible (it's a strategy game after all)
For instance here it would really help if the player can see stuff like how much it costs to link to another planet, how much resources your empire is currently requiring and how much you get per link established to a planet. This would also solve problems like making clear to the player that drain links are the only way to get more iron and thus establish more links.
Also as a small helper to new players it might be useful to block the player from starting a drain link from their home planet because that instantly locks your empire, found out about that the hard way hahaha
The music and visuals are nice, good job! (I also like that you already added difficulty levels!)