All of these things would be nice small additions and corrections to mobs, and taking the time to iron out these small perfecting details would do a great deal in the way of quality. I especially agree with your recommendations for zombies because it seems ridiculous that if they had helmets...
Not sure about the solar buggy, but I definitely think it would be smart to add Phobos and Deimos to Mars' skybox.
Galacticraft should try to make the sky (for all bodies) as vibrant and interesting as realism permits. There's definitely certain edits that could be done to improve the skybox on...
I'm not really positive with how space stations work, but I think each space station is its own dimension.
Anyways, glad to see you worked it out on your own. I'm sure if you wait for @Ezer'Arch, he can probably explain what's going on here.
I'd probably wait for someone who actually knows what they're doing to diagnose it, but from what I can tell it looks like they share the same dimension ID.
Also, if you want to share a screenshot, just upload it to this website and link it.
I'm assuming you mean a server host.
There are plenty of companies out there that will host a 24/7 server for a monthly cost.
One example is here, however if you do a quick google search you'll probably find plenty of others.
Very impressive and Sci-Fi esque. I don't think I have the patience to build something to this scale :p
Bravo!
EDIT:
Wish that Mars space stations were added, so that these could actually be built in orbit :/ Still cool, though.