(Part 1)
Well I can only base this on the information given by XIVCensus I can readily use. If I bugger up somewhere along the lines feel free to correct me.

* (Any reference to "Active" players, refers to players that have claimed the 3.3 story minion)

We currently have a total of 2,880 plots of land on each server. Plus apartments which I won't go into.

Averaging out the total active characters across all regional realms (rounded down to the nearest hundred for argument's sake) we are left with some food for thought.

NA: 15,000/server (12,120/server without access to housing).
JP: 7,600/server (4,720/server without access to housing).
EU: 12,800/server (9,920/server without access to housing).