Going "full retro" is very nice. Seeing your game played on an actual Game Boy is awesome. It's not a walk in the park, but it's not super hard either, depending on your experience. There are lots of resources here: http://avivace.github.io/awesome-gbdev
I make Game Boy games in assembly myself (although I haven't finished any yet... will try to do this jam though), but if you want to do it quickly (and not spend the entire month of August learning stuff) I'm going to go ahead and suggest checking out the ZGB engine. You code in C, and it has stuff to help you. There was a ZGB jam recently too.
It does use GBDK (Game Boy Development Kit) as a framework, which is not super great, but it helps you a lot along the way.