I think they've literally also just made the Kingdoms/Duchy's/County's/Towns etc so large that it can fit people in without the need for instancing. Like there's (i think) 3 to 5 Duchy's to a Kingdom, up to 32 County's and then up to 1,000 towns. And that's per server so it should be fine hopefully. Like in the APAC server chat, when referring to the towns, I've heard mention that they're a good 30 minutes apart at best, so that should give a semi-scope of size of the game.
They wanted to avoid instancing so that every house could look unique and since stuff is destructible, it would be too risky to group hundreds of houses into one instance.
In most cases, I'd reckon property won't be too difficult to come by, a part of being Aristocracy is wanting to attract people to the area you govern and entice them to stay. So I think you'll find areas that are willing to rent out land cheaply, and since you can explicit tax contracts with the Mayor/Count/Baron/Duke etc etc, you can come to an arrangement with them. Both perk and negative of dealing with Player leaders is that you can reason with them haha.
In terms of size, yeah I'm pretty sure land parcels can be broken down and distributed? But yeah, a Visual representation would be awesome too - I believe we should be getting something in June. They hinted in the recent Q&A to "Make sure you've got your pledge completed for land selection before the end of May"