Anyone have experience with Customer Centers? I'm trying utilize it and can't find much on it, other than how to turn it on. I can't find where to make a form external to customer center users

Customization of the Customer Center is extremely limited. Make sure you are working with a transaction form of a type containing "(External)"

Do you know where I can find that? I've been able to let customer center users create Estimates themselves, which is great, but the form looks horrendous and I can't seem to dictate which form is used for their view.

There is a form called Standard Online Quote. As mentioned the type is Quote (External). This is probably an inactive form. If you check the SHOW INACTIVES box you might see it