Elite is much more expensive, training hours are longer, and (I think) the risk of injury is higher. Sometimes girls don't go elite because it's just not what they want. Maybe they want a more normal teenage experience. Maybe elite just isn't a good fit for them (lots of girls try elite and then...
Yes the USAG website (usagym.org) is very informative. You might also be interested in Gym Mom. It's a book written by Rita Wieber (mother of 2012 Olympian Jordyn Wieber).
I think you can do JO and TOPS. Tops is ages 7-10. Hopes is ages 10-13 (?). Some girls do Tops and then go over to HOPEs as they get older. HOPES and TOPS are separate programs, but both have the goal of developing elite athletes.
The Karolyi's run an open summer camp at the Ranch.
On the Arête facebook they said a couple of days ago that she couldn't sleep and had to have eye drops/medications/treatment every hour. Now she sees light and shadows.
There's Lana's in Queens, Gold Medal on Long Island (Theresa Caputo's daughter went there), and there's something that's more of a recreational, open adult gym thing. It's called Gymnasticity. I don't know where it is though.
I'm curious about this too. I know in cheerleading it's pretty common to buy from the big name gym's pro shops (Top Gun, Cali, CA, etc,.) but I've never seen it in gymnastics.