You should be able to complete the signup process now from your cafe commerce admin.
Once completing the billing agreement, you can visit the "Domains and SSL" section under the settings tab for instruction on how to get your domain properly configured. Let me know if you have any questions.
I'm working on the large file upload issue, and should be able to get that resolved soon. We shouldn't have issues with digital files that size, so we just have to change some configuration settings to allow it.