This is a great game! I think it actually plays more like a very challenging city-builder than 4X, since the gameplay is centered around a network of production and buffs between stationary objects that you build, but the theme and aesthetic of building an interplanetary civilization works really well. I appreciate how hard it is too. It's not very fun when games just hand you success, but it's not fun either when you can't get any success or learn to play any better, and you've struck a pretty good balance here.
I've still only managed 3 stars on Challenging... not sure what I haven't figured out yet, but there's so much possibility and complexity with all the colonization options and techs and slipway strategy that I feel confident that with more learning and experimenting I could figure it out.
The main thing I'd suggest you maybe change or add is an undo button. I have made a few very costly mistakes that were not because I didn't understand what to do, but because I forgot my plan for a second or my mouse slipped. It would also allow me to learn how things work better without sacrificing important resources just to see what something does.