If you play mostly free, to be able to build a ship of a certain type, you need its skill developed to 20.

It is possible to buy blueprints for special ships from the shop, in which case I don't know if you need the base ship skill leveled up, but you'd better ask in discord to be sure.

I am also not sure if you need the skill fully developed if you buy a ship from someone else.

You also need Mission Control skill at least 1 to launch a mission, that is certain.