Modifying the store using eCart would not necessarily help you with bulk uploads. Currently you should be able to do a bulk upload by inserting all the correct data into the correct fields, but it would be somewhat complicated if you had product options and categories for the products.
The backend would either work the same or not work any longer depending on the changes you made using eCart. If you didn't make any modifications on how the products are used, you the admin pages should work the same. The front end pages should work the same, except for the payment gateway. Since PowerStore was created using our products, the frontend pages modified by eCart would only affect the checkout pages and the cart.