Do I need a separate eCommerce theme or a paste in script?

I am new to eCommerce. I already have a static site that give general information about my business. I want to add eCommerce. However, I don’t want to manually setup a products page in my current theme. I want to be able to just add products and have them automatically appear in a grid with all the necessary addons. Will a separate eCommerce theme do this for me or a paste in script? Also I want to show off my products in a slider whereas my current site have a slider on my business. Does an eCommerce theme automatically place products in a grid? Please help me know which is the simplest and best method.