If you have a friend w/ the rings you can just meet up online and he can hand them to you. I went through and just got them all on NG++. It's not as bad as it seems.
The toughest and most obnoxious thing is the Dark Moon covenant Rank 2, which you need for all miracles. If only the covenant actually worked and you got pulled into a game more than once every six hours, it wouldn't be so horrible. I still don't understand how there's people on the leaderboards with more than 1000 tithes. That just seems impossible. It took me forever to get 30.
Also, no, Princes aren't the last boss... and the hardest boss in the game is definitely the optional one in the Archdragon area.