To clarify somethings, you need 4 characters in your FC to purchase a house from the system. They can all be your alts though and can leave after purchasing the plot.

Secondly for those saying solo FCs shouldn't be a thing:

Blame SE for gating gil generating assets behind housing (Workshop,Submarines/Garden/Flowerpot)

A FC house can generate ~5m gil weekly as a low baseline with 4 max rank BiS submarines.

I used to be in normal FCs on different servers and my experience has been only very few people in the FC work/get rewarded for using the workshop.

The workshop should not be FC content but instead individual content.