I propose that for Paragon Industries expansion to Earth we set our firm's headquarters, research complex and manufacturing in a settlement that we'll design from the ground up, using hypermodular design principles and constructed in a way that will, eventually, culminate in it becoming a city-ship. Basically, our own corporate town/city (but not a city state, probably).
So what exactly is the difference between this and just attaching a trio of Factory III complexes (and attendant Barracks) to a Virgo? Scale? Are you proposing that we build a cluster of 100+ high-rise buildings on top of a permanently-floating platform, complete with municipal-scale transportation and other city services (water, power, trash pickup, etc), something that will probably require a few other techs, like Superalloys and Extra-large space stations? What would we even use the space for, given that
@Hoyr has given us a per-city limit of 3 factory IIIs?
Maybe you're planning on leasing the massive space out to other people/corporations? In that case you're basically setting PI up as a de-facto government, except you just said you aren't interested in creating an extra-national mega-corporate city-state. That would imply that whatever nation-state PI chose to locate that (possibly flying) city in would have legal jurisdiction over it, and could then create a city charter and assign a council to which the city will be beholden.
Somebody has to be in charge of the city, after all, and if PI isn't going to be in charge it would have to be someone else, someone who probably won't be able to afford the upkeep on the infrastructure in the early days since it'll take time to fully lease out the area in a city built for 1,000,000+ people.
What you're effectively proposing is that we build a (possibly flying) city, possibly for hundreds of billions of credits, and give it away to a country of our choosing. In addition to this being a terrible use of our money, this has the problem of being a massive political football. After all, there are still likely to be somewhere in the same ballpark of ~196 countries on Earth in the 2170s as exists today, and we don't have enough money to give multi-hundred-billion-credit flying cities to all of them. The resulting competition will result in a massive amount of publicity for us, but also a lot of controversy.
There may be an advantage in letting the various countries of Earth compete over who can give us the biggest incentive to locate our Earthside HQ in their country/municipality, but there's no way it's ever going to be worth the cost of building an entire city, and in fact given that we are primarily a weapons manufacturer it'd be all too easy for the publicity to turn negative. That's why I was planning on an alternative strategy of putting "small" 3.5 billion credit manufacturing complexes in every large city on Earth simultaneously, and then expanding to every medium-sized and small city on Earth when we have time/resources*.
Frankly we don't need to--and we probably don't
want to--build our city-ship on Earth at all. We can build Atlantis on another planet, or maybe in orbit around Sol or even another star, when we get around to starting our own colonies. I doubt we'll have a problem finding likely colonists by then, not if our other initiatives bear fruit.
*-
Ref. There are currently 457 cities with 1,000,000+ population, 1,063 cities with 500,000+ population, and 2,896 cities with 150,000+ population. Given that, I'd estimate that in the 2170s we could easily find enough cities to build 3,500 factory complexes on Earth, with admin buildings in each of the roughly 200 countries, without straining the population.
