Thanks everyone for your tips! I thought the cage was too small, so it's nice to hear you agree. This is the set up I have for him:
https://ibb.co/xzRKy12
I try to change the set up once he starts to get bored. I would take on any advice you have.
I've become obsessed with German cages and found this one:
https://www.amazon.de/M%C3%A4use-und...gateway&sr=8-1
What do you think?