It's all in the title.

Are people able to buy multiple houses? I thought they worked as an upgrade to the one you already own. But I don't see how having limits on the houses available would benefit anything otherwise.

I could save up enough to get an upgrade, but then end up not being able to get one at all?

You are able to own as many houses as you wish, even collect them if you so desire.

When you buy a new home you may not be able to move into it straight away. You’ll need to empty you current home first, and due to inventory space you could be waiting to sell some of your surplus to make room.

The houses do restock, but only Komodo knows when this is going to happen. When someone upgrades their current home they might put their old house in the market, so it’s worth checking in there often if you are looking for a certain house which isn’t currently available, or snap up a bargain if you’re lucky.

Keeping at least one spare house also allows you to temporarily move out from your current home if you wish to sell it to help fund your next house buy.

For example, if you currently live in the designer, and want to buy the mansion, but you are short on the required PC, and selling the designer would make this required PC. If you have kept your starter house you could move back into the starter, sell your designer and then you have the extra funds required for the mansion. Buy the mansion and move in - sorted!