Pro Sites, Domain Mapping, and Charging

Hello, We are setting up a website network for doctors. Doctors can buy a pre-made website specifically catered to their industry.

I am using pro-sites, and domain mapping and have that setup. My questions are:

1) Any recommendation on how they can input their domain on signup, and not have the pre-defined subdomain? We need to make it easy for them.

2) We have two packages, but no free level. When someone signs up with the default pro-sites they signup for free, then upgrade. Is there anyway for us to have them choose their package and pay from the initial signup?

So essentially we are trying to have them pick a package, put their domain in, and pay. Then the site is setup for them.

Any hints to accomplish this would be great. Thank you.