Selling digital files

Hello,
I have files (my design) to sale (already at Etsy). Planning to move as my own online shop. I have questions

1. Which template to choose for digital sale? (those that I checking are sample of physical)
2. What is the main concept using here? (for example, user login, purged and able to re-visit to re-download)
3. What's ever the answer of 2. Does that provided as a built-in option to select when building online-shop or that require some code editing?
4. Any requirements to open digital online shop (business license, etc.) more than personal web site?

Thanks in advance