Okay, stream of consciousnessy stuff.
700,000 people in ~= 50 km^2 is
dense - that's post-Renaissance London, Pax Romana Rome, or tenth century Baghdad. The minimum magically-assisted tech level must be at least as high as those cities or people starve; any medieval neo-iron age is a forgotten stage of prehistory.
A metropolis requires above all else a supply of food and trade, and neither of those are possible here without flight (
no roads lead to this Rome). Skymages extend life-or-death power over the economy. Thus they're the sole powerful mercantile class, if not the ruling oligarchs; they can't be cloistered hieratics and still do their jobs. There need to be lots of them too - perhaps as many as one person in a hundred is at least a minor hedge wizard.
Given that, there probably aren't skymages per se. Some mages still specialize in maize desmutting, weather tampering, golem craft, diamond forging, and suchlike, but if you can't lift a magic rock you're probably a peasant. Disappointing and inexorable?
With forklifts a definite part of the picture, we can look at aqueducts: simple machines that need building (and might need maintenance) but don't need a pilot. It's impractical for a resident of this city to go dig peat, and it's goofy to jaunt down to the local Pyromart for a packet of
Suddenly, There's Plasma! (c), so the household hearth contains an everburning swad, your compluvium fills itself, and nobody gasps to see golems or zombies handling all the unskilled labor - like the aforementioned milling and cotton ginning. So the folks in the peasantry are kinda-bourgeois crafters dwelling in a deliberately manipulated microclimate.
All of which makes the capitol city a tempting target for needy barbarians - where do they live? If the floatstone culture is isolated, are individual cities conducting internecene Medici versus Petrucci style warfare? If the culture's not isolated, is it enough just to build your house on the most aerially fortified stronghold around, or do you need more than perfunctory experience in pyromantic firebombering and anti-siege engineering?
And this:
I think that other nations pretty clearly have competitive advantage in metal work and agriculture.
sounds important too - how can you characterize in terms of what's scarce when saffron and strawberries are relatively abundant compared to wheat? Is there anything besides raw materials that people can't reasonably get enough of? Land is lacking and the culture is too technolgized and interdependent to be readily exportable, so if people aren't killing each other (a lot) there's going to be overpopulation. That may not be enough.
Am I barging in here, by the way? Might have asked that first, but it'd require, you know, foresight.
