Not only is there a quite complete Help menu, but there is an aggressive popup at the start of the game when you first play it, to make sure you know about it and advise you to have a look at it (with a big button that takes you directly there). So, yeah, you have to do a little bit of reading, or figure things out yourself by trying the mechanics, it's not rocket science either. On top of that, the game is not punitive and there is no "wrong" way to play it, because the main idea is freedom. That said, I am fully aware that different people have different tastes, and you're probably not used to play sandbox games.
At one point the demon girl will ask you to do something particularly evil, and after you do it the angel will show up.
It kinda is the point, you were complaining about finding a picture "ugly". The beauty stat is indeed primarily just a number, that affects different things in the game, and that you can affect yourself with spells and different mechanics. As for the folders, since the districts are of different tiers, the girls in city center will be on average more beautiful than the ones in the alley, but again you might disagree in some cases as it's pretty subjective. For daughters, I changed the system recently to make them district-independent, and they are all considered beautiful, as it is assumed that you physically like the mother (you made babies with her). This fixes an old annoying issue that people were having with missing pictures, when they made a lot of daughters from the same girl type and the same district. So yeah, the best option is to replace whatever image you don't like. Also keep in mind that nothing is definitive, the game is still in "early" development.
Not for now, the same has been asked for "tattoos", I will probably allow that kind of stuff in the future by making physical traits influence the picking of scenes, but replacing
all scenes as a modder will take you a huge amount of time, even if you make it one scene per position/clothing and girl type, we are talking about hundreds of scenes that would need to respect the specific physical trait.
These seem to be very nice pictures you added in old canal, don't hesitate to share your custom pictures as a .zip (if you want!) so that people can use them too. I also could add some of them to the base game