1) There are two simple animations, but I've only been able to get the first -- either the developer didn't add a way to view the second one, or it's really obscure. Every so often you can see the couple flirting in the hallway, with speech bubbles indicating that the man is propositioning the woman. Later the same day you'll be able to peek on them having sex against a wall. If you ever miss an opportunity to peek on them (due to spending time with the main girl, sleeping, etc.) then you're permanently locked out and can never peek on them again. (The possibly-inaccessible second animation looks like reverse cowgirl while he chokes her.)
2) That's exactly what the rewind button does, no? Assuming you mean day 2 of the onsen events, rather than day 2 of the entire game.
3) I'm pretty sure the only thing 100% pregnancy does is let you wake up Shota during the final scene. I've seen the options to call Chiho to the men's onsen or do petplay both appear around day 6 (if I recall correctly), even if she's not pregnant yet.