There is no way to pause the game. Animals should stop periodically (briefly) when running around. Get a bedroll for each of your party members, and you can use it after combat whoever is active when it ends (add it to the hotbar).
The levels tend to get larger later in the game, and the farther you get into each act, the more data there is to keep track of.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
You can move saves to another location, or otherwise back them up, though if you have cloud saves enabled, either disable it, so the 'missing' saves do not get downloaded when you restart the game, or copy the saves elsewhere, and then delete them in-game.
In Galaxy cloud support can be disabled either globally (click on the GOG.com button and select Settings, and then Features) or just for this game (with the game selected, click the More button and select Settings, then near the bottom unselect the Cloud saves option).
There are no such mods, AFAIK.