I have a broken TI 83 calc in the marketplace somewhere that has a broken LCD. Everything else is fine, all the buttons are there and functional and stuff like that, only the LCD has a lot of dead pixels which makes it unusable for actual calculating but perfect for a project like this. I don't think it would be too bad of a first project, just fitting the GB into the case and soldering the controller parts to the calc board. I haven't made a TI-gameboy though so unsure if you'll have to cut some motherboards down or not.