Matt - my advice: hold off. This is a project that we have been working on since September. We're only a week or so from bringing everything to life.
You'll notice that all the big blog posts from September forward have been about big releases that were all needed for this, including payment gateways, UI improvements, MIurl.cc, and a revamped portal setup process for HTTPS urls.
Once we put it out, you can then customize to your heart's content. You'll be thankful that you waited - trust me.
In the meantime, make sure you setup your payment gateway under Customize > My Account with Authorize.net, Intuit Payment Solutions or PSI Gate.
Paul