Yeah, there are many things need to be fixed or improved, actually I've already noticed some of the things that can cause bugs/crashes before submitting, but unable to do that due to some basic mechanisms done while having around under 5 days to submit and also have to add some contents for "end-game stage".
As for the crash while you're trying to fix the spaceship, you only have a thruster crafted in your inventory and you get close to spaceship and press E to fix, sadly that I can't reproduce this bug as you did and pointed out for now... The crafting system has a big flaw currently, it will iterate through your inventory and check if you have one of these resources, it will craft same item multiple times for you if you have more than one resource that is listed in that crafting recipe.
There are other things that you've pointed out such as to limit how deep the player can fall down and better placing blocks control, not sure if I'm mistaken your points, one approach I have think of is to control the way of the world generate so that it didn't vertical gap too much, the placing block control sure is not very convenient and I've yet to find out a way to fix it for now.
By the way, I'm really, really appreciated your comments and feedbacks you've given here, thanks for your playing!