Thank you all for your comments and feedback!
Chet Thaker I would first define the MVP — talking about the definition here, in the form of a prioritized set of user stories. I would then use this MVP definition as a guide to decide if and what prototype is needed. The process of defining the MVP should be fast enough; and guide you in deciding what needs to be prototyped and what particular technologies need to be proved — if any. In general, prototypes (functional or not) are key in this process. Happy to answer any particular questions. -George