Nice idea, but i got alot more for it.
but i think that for it to work, and be fair, space colonies would have to be different from planets, they could be ship building centers or trading centers that could be used to trade more conveniently or create ships if they are needed, the tech for it would have to be its own technology line. and though it could remain a regular constructor module, itshould be something like an advanced constructor/colony module, which would require alot of maintnance when created, like you said. basically a space colony would be very expensive to upkeep, and difficult to profit from, and with technology it could get cheaper and cheaper to maintain. also theycould have support ships that you could set to be built automatically or manually, these support ships would also cost to maintain. and they would cost less to maintain the closer the colony is to a planet, as well as if you configured them manually, to cater to the specific needs of the colony, such as amount of food, and building materials, as well as things such as waste management, consumer products, or even ships, which could be stored and shipped back to the support ships destination. you could also manually configure which planets support ships travel from a space colony to. if left on automatic, the support ship would simply go to the nearest planet. which if it is a poor, and low resource planet, would cost you more. while if you manually chose a planet rich in resources, it would be extremely cheap to you, and could save you money from the planets maintnance costs. as for food transport, support ships could take excess food from your planet, or food that you manually set aside for it, to the space colonies. and for ship building, support ships could carry hulls built by a colony to the set planet to be turned into ships, this could make ships faster or cheaper to build, and support ships could also be used between regular colonies as a from of intra-race trade, which could help your empire to become more productive, the benifits of inter-colony (not intra) support ships would be greater with different forms of government, for example, an empire, which provides the least production benefits, and keeps colonies close together under one rule, would provide some benefits, because it would make colonies even out happiness. support ships would transport morale, in the form of different things to entertain your populations, but because of the fact that the colonies are not as self reliant anyway, would have much other affect, while with a federation, they would make colonies they travel too more productive because they are carrying leftovers from other colonies, in other words excess, which colonies could put to good use, and they would be more effective then with an empire, because in a federation colonies are more seperate and independant and less interconnected, or aware of each others resources. with a federation, basically support ships would become more necessary or the unity and survival of your colonies. i've written too much and gotta stop now. at this period. right now. .