Heya! On the very start of the village (on the bottom right) you can go into a building that is a hot spring, talking to the purple fairy in there progresses the main story.
There is no plans for a android version, but I think it might be possible to play the game on it with Joiplay, no idea how well the game works on it though.
Currently these are the only giant boss fights in the game. As for the soundtrack, 95% of it are tracks that I bought to use from the rpg maker store, the exception currently is Viscous boss theme, that one is original <3