In order to purchase an Estate, you must have a Maid Chief (including Chambermaid Chiefs) in your hand. When an Estate is purchased, a Maid Chief card must be placed underneath it in your Private Quarters to tend the Estate. This Maid Chief cannot be the target of any Illnesses or Bad Habits.
If an Estate is destroyed by an opponent using the ability of Victoria Calderan, the Estate is returned to town, and the Maid Chief tending it is placed in your discard pile.
Purchasing an Estate is almost always a good idea if you're eligble to do so. Ideally, you can use it to chamber a high value Maid Chief, but you can even use it to remove Chambermaid Chiefs if you're high on Love but short on Servings. And it's worth 2VP either way.