The answer is yes to all of the first batch of questions, and no to all the second batch of questions. The regular license allows you to create end products for your clients and charge them for doing so. The license is for life, so they can use that site for as long as they want, and to sell products from.
That applies to regular licenses and extended licenses. The only time you need an extended license is if people have to pay to use or access part of the end product. So in your example… people don’t have to pay to access the site, and even though they have to pay to order products, those end products (let’s say they’re clothes) weren’t created using items from Envato, so it’s all good. An exception in your case would be if the client set up some kind of VIP area of the site, where people had to pay to access certain pages with super special deals. That would require an extended license.
But for most ecommerce sites that people create for their clients, a regular license should be fine.