Hmm... Personally I don't see how "up and down" could create true anticipation... I mean, if she fucked a dog (as one fellow "forum dweller" proposes), she fucked a dog and that's something I won't be waiting for because it already happened. If I was writing a story and wanted to have some hard core scene very early, I'd make Lily sumble at someone else doing something. That way I have my hard core scene, she doesn't do it herself (I can still wait for her to be corrupted enough), and if the player decides she stays longer to watch, she 1) becomes more corrupted 2) can get into trouble for peeking (she was told she musn't go to the basement, right?).
As for games with dark topics and quite good progression (although not perfect) I can recommend Personal Assistant - Blackheart edition. It can be really dark but the more drastic stuff with main characters doesn't happen early on.
Well written bestiality can be good in this type of game. I don't need it, but I don't have anything againt it if dev decides to put it in the game. Especially if it's optional, although optional content creates problems for the dev. Either optional scene doesn't have any impact on the story (a bit unrealistic if we are talking bestiality - I'd say something like that would have impact on Lily), or dev has to write two different versions with and without optional scene.
Having said that, it's easy to logically introduce bestiality into VST. There is a tag "slave". Is it so hard to imagine that enslaved Lily is forced to give a show with a dog somewhere in the secret dungeon of the strip club or in Susan's basement?
My advice would be to ask them directly. That way you are safe for the future: you have confirmation from Patreon that it's ok. As for national laws, I don't think there are any that apply to computer generated images. You can always put a disclaimer at the beginning. Something along the lines: "if the content of this game breaks any laws in your jurisdiction, please turn off this game immediately".
BTW,
Eromantis do you plan for Lily to be constantly forced, or do you plan for her to be more and more willing to do lewd things and only forced at some points, when she finds it more difficult to cross another limit?