Wow, this is a very cute game. I had fun with it and it inspired me to make my own GB game.
Sure! Use a notebook for notes or ideas (I used a lot of sticky notes), use MS paint for pixel art if you don't have access to other pixel software, learn how to use the color palette functions so that your game contains many colors- my game only had like 4 colors when I first released it because I didn't know how to add more colors in until I taught myself how to use the palette functions (if you're using GB Studios).