What base level do I need to go to launching center?

Any base can go to the LC, the game sets no limit on that.

If no one is fighting for it or attacking from other states, you can hold and win the LC, it just takes a smaller base longer (occupation time).

If there's fighting it depends on your opponents - their size, skill and strength.

Smaller bases can sit on the edge, keep shields, and send missiles or nuisance attacks - that's a great way to be helpful if you can't actually fight your opponents.