Yes, gallery is in the game. You can also use cheats to increase corruption (click at the paint in the bedroom).How to access the gallery?
Ingame from the achievements tab?
Cant play extra scenes there
720p version file named FashionBusiness-EP3-v12-720p-pc.zip
1080p vesion file named FashionBusiness-EP3-v12-Extra-pc.zip
So, maybe 1080p is really Extra version I don't want to download 12 GB to check this.
Mod should work anyway on 1080p too.