a) uCoz - Yes, that's right.
b) uKit - Currently you cannot buy a template for uKit, though yes, you can customize the existing template to certain extent. You can also order a custom website from our team who will customize the website according to your wishes.
Ecwid states they charge no transaction fees https://www.ecwid.com/pricing From what I can see they use 2Checkout to process bank payments and it may take fees. Here is a quote from Ecwid forum:
No Transaction Fee means that Ecwid doesn’t charge for any transaction in your store.
2checkout is one of payment systems integrated in Ecwid, which allows you receiving money from your customers. The percentage that 2checkout takes is the same whether you use Ecwid or other solution. It also doesn’t depend your pricing plan.
c) uShop is basically the uCoz's shop module. It has a separate button on the home page to make it easier to find for those who are looking specifically for an online shop.
I'm not active on the forum anymore. Please contact other forum staff.