I mean your question is kind of a trap because my definition of acceptable is probably different from yours but my answer is that multiple properties was acceptable before the rules changed. SE obviously doesn't want to punish or take away from players who weren't doing anything wrong at the time they purchased the properties. When it comes to "shell FCs" I think the buying a selling of FCs for the purpose of flipping housing should be against TOS as i consider it an exploit of the system and of other players.