Hello there.
1. Yes. Go to the game folder, and in the "www" folder, delete the entire "save"-folder. That gets rid of all your save files and game settings, but it's not really nessecary. This is an RPGMaker game, which is an engine that does not carry any information from previous playthroughs over, or rather there is no option to program that in. Which means, each playthrough you begin in an RPGMaker game is always a fresh start. When you start a new game, it's always a new playthrough, and if you ask Omega Death to bring you to the gallery, you are merely teleported to a version of the gallery where everything is already unlocked. When you find the rewatch house normally in the game, you'll find there's only available what you've already unlocked this playthrough. The reason for the full gallery you can go to right at the start of the game is that when the project was still young, there used to be a problem with carrying save files over from older versions of the game. So, to let people see the new content right away each update without having to restart over and over again, the gallery option right at the start was added.
2. Unfortunately, there isn't. Those files you mentioned change the language of the game editor, but not the game itself. English is the only option.
3. I can't speak on Spedu's behalf about what he might add, but there is a caracal char in the game you can have a scene with. It's not the same kind of cat of course, but the closest thing we got right now. And yes, there are two bears you can bone so far. One animated scene, and one regular scene that's currently only available in the Patreon version.