I searched for this in the forums but didn't find an official answer.

What are the guidelines for whether a site is considered to be commercial (and therefore need to pay for a licence)?

Do you actually have to be directly selling a product to be classed as a commercial site, or would displaying affiliate banners and links also count? I mean banners you place yourself and (hopefully) get paid for, not ones that directly pay for hosting.

Is there a certain amount of leeway for startup sites that are planning to make money but haven't grown enough for that to happen yet?