Thank you for the nice words
The cheat codes can be found in spinoff games :
https://nymphokyun.itch.io/futabirthday (after completing a branch you'll be offered a cheat code for SB)
SB // Orks Ryona BBC (will be released this week)
I believe others can offer a better guidance on save files, however be aware that loading a completed save file doesn't mean that you'll see all the h scenes. For story mode, they don't really repeat, and are unique to that story progression point. For free mode, you'll still need to redo the tamings to see those animations and spend in-game time to access special events (Halloween, Xmas..). In case you think you've seen all the h animations or game features, check the Book's Help to see if you haven't missed anything ;)
You can also check the walkthru videos above (in game description), maybe they'll be of some help