Hello, mate.
I've been making a mod in recent years and I'm having serious problems with graphics. I would like to take the same approach as you, can you tell me which software you used?
For editing Graphics im using Clip Studio Paint, but its not a freeware i bought it a few years ago as i tried myself around with drawing digital stuff. But ususally if you look for Open Source Software GIMP also can satisfy most graphic editing challenges
I used Night Studio Creator, and its not as easy to make a sprite from it. As i didnt need much animations for the reactor but for a building with a lot of fancy animation, AI isnt far enouh for that.