Thanks for playing.
Not having audio wasn't much of a choice as I don't have a good experience with sound design nor I have any person to help with making/adding BGM to a GB Studio.
For the graphics, I drew them normally with drawing apps and converted them to GB style pixel art using this tool: http://yrlab.zatunen.com/webgl/gbpic/gbpic.html
I wish I had a real Game Boy, if it's not too much to ask can you take a photo of any of the screens with characters on them? I'd like to show how it looks in a real Game Boy device to a friend.