Thank you so much for your kind words, happy you enjoyed the demo. It really means a lot to me and boosts the determination to finish the full game even more!
It's hard to say exactly how long the whole story will end up being. Consider the demo to be approximately 30% of the entire game.
It's great you've been noticing easter eggs. There are also little refferences to, e.g., Undertale and Skyrim, and many others (perhaps not so obvious though).
Amazing that you finally find the treasure! It is pretty crucial to the old guy's arc, storywise. Also you can try to solve the puzzle with the small birds in the city if you want.
As for the Carnival points - consider this to be a special attack meter (like in fighting games or TPs in RPGs) and not your typical MPs (nevertheless, you can still fill up you Carival gauge and use Carnival-based abilities outside of the battle but you can't keep them for a combat - and vice versa). I wanted Carnival points to be that way to compliment the lore, that chaotic, under-researched nature of Carnival energy. On the other hand, Feint (purple) gauge works as a regular MP gauge.
And my special gratitude to you acknowledging the language, that means a lot!