I'm glad you have beaten the game. About the last hidden room, all materials are able to collect inside the castle, so you will not miss them. And about the sequel, it is still under development but the process is kind of slow because I have been working on it all by myself. Currently, there is a demo with a small percentage of the story is ready to try. If you feel interested, please send my a private message on Itch here, or through my facebook page. Thank you.