The bigger the cage you can accommodate/afford the better. Spike and Peanut are in a Little Friends 160 x 80cm, I really like it as it's very stable and strong. Rusty and Bracken are in a 3 x 4 C&C which I love for it's versatility. There's pros and cons for both types of cage, it's down to personal choice really. I don't think you did the wrong thing getting Mo a friend, it sounds like they get on quite well for boars! I think they will improve whe they have more space.
Good luck at the vets, hopefully it is just a patch of dry skin.