Hi, sherkin! Thanks for asking!
Actually, the auto saves are there--if you go to the Load screen, you see there's a "<< 1 2 3 4 5 >>" icons right? If you're on page 1 and click the "<<" icon, you'll be directed to the auto save files!
you can also use the ">>" icon to go more than 10 pages. I like to think of this as a hidden function that users can discover by themselves--but my bad ^^;
As for the Antagonist route, once you get all 3 good endings, the mirrors should turn clear on the main menu and a black mirror will appear. Once this happens, just click on "New Game". You'll notice there are suble differences and you acn now pick the Black Mirror! this means you've unlocked the Antagonist route! But of course, if you choose the other mirrors, you'll be directed to the main 3 routes.
As for what mirror to choose in the beginning... you can choose whatever you want! It won't lock you to a bachelor so early, but if you want to pick the antagonist route, you MUST choose the Black Mirror. It's the hardest route of them all so I suggest to save often~ ^.^)/