Respawning enemies is probably the worst idea I've heard.
After I have fought enemies once and cleaned the area, I have no desire to do it again. It is annoying in every game I have played.
I don't care completely if the player could leave the area to rest, everyone plays as they please. Forcing you to clean an area in one rest is stupid.
Another thing, if you kill again enemy should drop exp and loot? If it's not even worse. Spending 3-5 minutes fighting with which you literally have nothing from it is annoying.
If you want to play like that, please do not force others to do it.