Maybe they replicate the whole population... ;-)
Isn't it possible to diversify between homeworlds and colonies? Maybe colony populations should be kept much lower. Colonies are, in fact, outposts or stepping stones and will only reach a similar status as the homeworld after many more centuries. I like the idea of ferrying around population of the homeworld to a colony. Maybe each colonyship committed to a colony can raise its max pop a bit? An empire should not grow through colonisation, but by integrating other homeworlds of minors (or majors).
Terraforming should be done in combination with science vessels and transports or construction ships, after a lot of scanning, with research bonusses. And one planet at a time.
I am more the eXplore and eXpand kind of guy...

There will be terraforming. You will be able to change planet type one or two times. Desert-Terran; Volcaninc-Desert-Terran; Barren-Volcanic-Desert, etc.
These are just examples, we will decide what types of planets you will be able to terraform to some other type, and it will depend on your tech level.

About colonies, they just take some time to develop to the level of the Homeworld but canonically speaking in Star Trek there were important big colonies like Deneva colony, Alpha Centauri..... Plus the empires that are not very open to aliens like the Klingons and the Romulans would have a more difficult time expanding.

There are examples in Earth's history where the colonies grow to be larger than the founding nation. I would not like to limit the colony to a lesser potential. I would like it if taking the "home" world did not mean the end of a race in the game. There are games like Age of Empires where you can set up a new home base. Unfortunately the capture of the one home world rule has long been coded into the game and it can't be change for Supremacy.

Wait, if you lose your Homeworld, you lose the empire?

That's going to change AFAIK.



Not a good idea, since new pop in a system is free... that is, colony ships don't take pop from the system where they're built.



If colony ships would cost pop, I agree.



Replicators don't make stuff out of nothing. Even if they used materials found on the system, you'd need industrial grade replicators to build all the stuff. Lots of them. And energy to power them, which you don't have. Getting the materials for the reps without having a mining system in place, and infrastructure of any kind... and building farms on barren systems, etc.
Sorry, not convinced.

I kind of agree with this. Making colony ships actually cost pop from the system that builds them could be interesting in this respect.



That was the initial plan I think. I think it's changed though. I hope.