Current: Freelance designer, researcher, startup consultant. General Assembly instructor, Thinkful mentor. Past: AppNexus, JOOR, Advomatic, UbiquityLab and many more. Edu: Domus Academy Master in Interaction Design, Claremont McKenna College BA Government
It sounds like you already have a good idea of how your users will interact with the service. The best idea is to figure out (1) what tasks you want to test; (2) create realistic scenarios that you can have users "imagine" they are in the middle of and (3) design the prototype to fit those tasks and scenarios. If you try and prototype the whole thing (or most digital services) you'll no longer be doing it rapidly!