The current demo is Chapters 0, 1, and 2. Dunno how many the full game will be.
I don't know what exactly triggers Gimdin's Special Item, but just keep visiting Gimdin and it should happen eventually. I do believe the Gimdin events happen in a particular sequence, and it's a later one. Volga's Ass Play can't be completed until you get Gimdin's Special Item, but all you have to do is click Sleep at the inn, which would probably happen eventually anyway (maybe not if you're right at the end of the demo, since you can only click Sleep during an Intermission, not during a main quest, and it ends after a main quest).