What is the rule of the limitation should I apply for the music when I use Famitracker to respect the subject of the Game Boy ?
Do you have any other recommanded music software ?
If you're already familiar with trackers, check out furnace. It has support for MANY different platforms, Gameboy being one of them. FamiTracker will do the job, but if you want to go truly authentic, Furnace is recommended. If you have access to a DAW and prefer piano rolls, I'd recommend Soraboy VST, which can be found on itch.
Best of luck!