I would probably start with a top down space shooter or something like eve. You can build out your quadrants from a top down view. You will also start the process of physics. How the ship moves in space , acceleration etc. Than I would probably move towards in ship mobility. where the player can switch from cockpit view to walking in their ship. Then start start with FPS shooting. and than move towards docking and building space ports and than building planets and slowly move from there. Try to do the most minimum first. But finished game. If I had a good game designer, I could build a space similator easily.