If you have only limited conquest in mind, like taking over 1-2 civs, you might want to manage the diplomacy a bit first. In Civ VI, when you make a friend, it is forever. Meaning, for the meaningful part of the game. Declared Friendships, once signed, will always be renewed irrespective of your further actions, as long as you offer the renewal on the turn of their expiry. And they cannot be broken. And Declared Friends cannot go to war against one another. So if you have a DoF with civ A who has alliance with civ B and you attack civ B, civ A will do nothing and will duly accept renewal of friendship on the turn of expiry. Only when the game approaches the end, AI starts rejecting DoF offers, but then they might come and offer it themselves next turn or so.
As for -5 DF penalty, well, you can try and build a pagoda for each capital you take, to even up your karma points somewhat