eCart 5 is completely compatible with eCart 4 so if you have any server behaviors that were created in eCart 4, you should be able to modify them in eCart 5.
eCart 5 includes the manage color UI which helps you in modifying the colors of your cart page, and you could also save the different cart layouts as a preset. There are also new layouts that got added.
eCart 5 allows you to apply to server behaviors with attaching them to a button on a page.
eCart 5 will create the database for you and add the bindings for order management.
eCart 5 includes order management presets.
there are a few more, but those are the major ones.
Let me know if you still have any questions.