Everything that you can do on PC you can do on GCN. The only real differences are longer loading times as well as less hint monitors on the hunting stages. Running on GCN wont put you at too much at a disadvantage as once you get a sub 50, the leader boards go by in game time, which you can manually calculate. Also, even on PC there is still the problem of the shared button layout despite the unused buttons. If you ever need help the community will be more than willing to help. Feel free to join the sonic speedrunning discord, the link is in guides. Good Luck learning and have fun.