I'm about to train my construction skill up and redo parts of my house, and add a dungeon. I've never had a dungeon or throne room in my house before, so I am wondering if I turn PvP mode on in my house and leave, will it still be on when I return? Or do I have to manually turn it on every time I enter my house? I'm trying to determine where I should build my throne room based on this.

When you enter your house and it loads up, PVP mode will not be active. You trigger it by pulling the lever in the throne room. Once you've done that PVP mode remains active for as long as the house remains loaded. If you leave the house and no one else is inside, the instance will get deleted at some later point and you'll have to reactivate PVP mode when you enter the house again.

 

As far as I know, PVP mode can also get deactivated when you get killed in your own house. I'm not too sure about this though, as it's been a while since I went to a house party.