Product archetypes is a fancy way of same form factors. Usually some quick explorations showing where internal components might be located and how that impacts the architecture of the design. This might include use cases that show where relevant grips might be, interaction patterns, things like that. Basically it is a phase to get stake holders aligned on some of the critical parameters and lock in some basics about the product.
MP1 = Mass Production 1, the first run of product. Sometimes clients only want concepts, sometimes they want to go all the way to production files, sometimes they want design direction through the first prototype (golden sample), sometimes all the way to MP1. Different clients need different things based on their capabilities and band width. I try to show them the entirety of what we can do and then work with them to figure out what they need.