I bought a mansion "on my lonesome" and use it every day. In fact, because it's near a market board, I rarely even need to leave my house's area unless I need to turn in a quest... I let three other people use the house too, so that they don't have to buy their own. And even though my FC also has a mansion, a lot of times people gather at my house instead. There are plenty of people who utilize their personal housing very well.
Speaking of personal vs. FC housing: the NPC in Shirogane confirms that both FCs and private owners will be able to purchase houses in the area, in such a way that leads me believe there will be no delay between when FCs and individuals can purchase.
