yeah gets huge and will probably outlive you. I don't think it really matters if they are alone or in groups.
They need a vegetarian diet, w/ a lot of dark, leafy greens (collards, turnip greens, etc. NO ICEBERG LETTUCE) and fruit. At least that's the jist of it...I don't really know their specific nutritional needs.
High temps (80-85 ambient, 95-100 basking) and low humidity (I think) will keep them happy. They will need an ENORMOUS amount of room eventually as they grow very large.
You could conceivably keep any desert reptile with similar requirements with a sulcatta, but I don't ever suggest mixing species when it comes to reptiles.
That's as much as I know, I don't have much experience with sulcattas or tortoises in general. Your best bet would probably be to do your research BEFORE you order animals next time. (not that I've always followed that rule...mabye I shouldn't preach
)