Why not a pressurized facility? It works better.
For your fleet, I would make it a goal to build as much as possible. Think of it like playing an RTS. First, you eat one asteroid and build level 1 ships, then...
And before you know it, you have a couple of warships, and all your manufacturing is in space.
Remember: There's no reason to ever land on a planet. Once you get all your infrastructure in space, there's no reason to turn back.