I expect them to be reasonably basic. Certainly not like NMS style.Such individual designs must be very basic then, otherwise the main server would go down in a puff of smoke in no time. Or why do you think did we got paintjobs instead of some kit to individually create our own ship designs? Can't be the money alone as single elements of such a 'paint kit' could still be sold (and would arguably generate more income than the current boring paint jobs).
As to the server. If NMS server can cope with what it does, I can't see why Fdev servers can't.