So going by https://na.finalfantasyxiv.com/lodes.../housing_land/, the restrictions for FC purchases are:
  • 4 or more members
  • Rank 6 or higher
  • Does not currently own an FC house

Also, going by https://na.finalfantasyxiv.com/lodes...t_freecompany/, there needs to be at least four members to found an FC.

The last thing that's missing with this is enforcing that all FCs have at least four members, or they have a week (or a month) before the server automatically disbands the FC because it is too small.

IMO, this is a necessary feature for FCs that should have always been there.