What has to be done to house Sulcatas together and how close in size do they have to be? I imagine that my guys differ to much in size right now, but once Goomba is bigger I'd like to house them in one large area.
It goes on a case-by-case basis. Some sulcatas get along just fine with more than one in a pen and others absolutely WILL NOT tolerate another tortoise in their pen.
Several years ago I fostered a group of sulcatas while the owner was making changes and repairing their yard. They were all wild caught, full grown sulcatas consisting of about 3 males and 4 females. They lived together in my back yard for about a month or so with no fighting at all. Not an exceptionally big back yard...just normal size.
My Dudley breaks down fences if he smells another tort nearby. Doesn't matter if its female or male, large or small. Because he's bigger than I can handle, I've never allowed him to stay once he's broken down the fence because I don't know if I can handle a fight to break it up. But he has "death" in his eye.
Yvonne is right. They are all individuals, but there are still some reasonable generalities. I have a super aggressive juvenile female (this is almost an oxy-moron), and on Yvonne's advice I moved her in with my adults and gave up trying to make her stop attacking other juveniles. She tried to bully the adults that were 10-20 times her size, but they mostly ignored her or just walked away.
In general groups stand a much better chance than pairs, regardless of sexes. In general two males will not get along and if they do it is often temporary. In general, a large enclosure with lots of nooks, crannies, visual barriers and hiding spots will increase the chances of a peaceful coexistence.