How does Commerce handle situations where a client purchases say 10 items of the same product at once? I see that I can add the dimensions and weight PER item and Commerce will calculate shipping via EasyPost based on this but it will estimate the same amount of shipping for 1 item vs an order of say 10 items. This obviously would be wrong.

Is there a setting for this? I checked but nothing really stood out. If combined shipping is not allowed, this would be a deal breaker for me. =(

It all depends on how you set up your shipping methods. You can have “combined shipping”, but you need to pick one of those methods to calculate this. 

Oh I see. I'm going to have to play around a bit with that criteria. I'm still trying to figure out Commerce.

Take a look at our guides here. This may help you to navigate the commerce application