I think the best way to implement the customisation system would be to add a "Don't Starve Together" kind of system.
If you're unfamiliar with this system, it's pretty much you play the game as you do but every now and then a little present symbol appears in the top left corner of your screen. When you click on it it unlocks a a new piece of vanity for you to equip across all your saves.
If you changed the way it works a little so instead of just randomly getting them you could find suits on like other planets in crashed ships or something that would be perfect because this would promote exploration by a ten-fold because who doesn't want new space suits?
I understand one of the major drawbacks would be your character artists would have a lot of work ahead of them, so to combat this I present you with another idea: The ability to find different colour palettes to equip on your suits. This in combination with extra suits would bring a unique feel to your own astroneer and make him feel a lot more personal to you.
Keep up the good work! ~ Melon