I expanded the rom using HxD, using one of its functionalities that adds "00" bytes, therefore creating new free space.
Thank you! I tried my best recreating the maps, but I'll add more variety to the tiles. About the music, I used something that allows for higher quality music, but takes up a lot of space as a result (importing WAVs), so it does sound similar. It is the reason why the rom is bigger indeed.
Yes, WAVs fade out once a battle starts. There is no fix AFAIK.
EDIT: I will probably be remaking Chapter 1's Map at some point to make it more accurate to the game (also because I didn't make it, and I want to make my own map for it)