Powerstore3 and ecart integrated functionality

I am looking to integrate, at this time, what I think is only a small portion of the eCart functionality within my PowerStore 3 site. Really all I am after at this time is the enhanced shipping and discount rules that eCart5 provides. With that in mind, as I review all the documentation around setting up eCart within my Powerstore3 site, do I really need to follow thru with step 2 (add to cart buttons) and step 3 (your cart display) since my PowerStore 3 site already seems to provide the functionality that is described in the steps I would be doing within eCart? Am I missing something that eCart is doing in these steps that PowerStore3 is not???

If PowerStore3 is doing this functionality already (which I am happy with and do not see any reason to change), can I simply drop down into step 4 (checkout pages) and implement the discount and shipping steps identified there via the wizard? Am I going to screw things up by not having done steps 2 and 3 (which seem redundant to me since I have the product detail and summary pages already in my PowerStore3 site)?

Thanks for any advice on this?

Steve