Problems in creating a space sandbox

basic idea i have:
I want to create a little sandbox where you can fly around in space and explore planets (not to the surface just yet). and have other idea’s i would like to add to it but i’m still reading up on it.

Problems:
I’m not much of a fan of having a Hit point based game and would like to know how to make the character meshes take damage if it e.g. the engine or O2 compartment get hit causing a loss in engine power or O2 until fixed which will have a timer until repaired. (this i have little to no idea on how to complete this)

another problem is that each planet is going to have it’s own unique gravity. this i do not really have an idea on how to do, i’m still fairly new to unreal and i’m still reading on how to work the software and coding is not my strongest point so any help here would be awesome!

I’m working on the character model in blender at the moment and as said above any help would be awesome.

thank you!