I used the gem Wicked to assist in creating a step-by-step flow.
Due to the limitation of creating a User at the end of the flow only, I created a UserValidations class that validates each step of the flow, saving the data in session. At the end of the flow, I unmarshal the session data, trim it to only the specified fields, and create a User. The User model only verifies if the necessary fields are filled - the UserValidations class validates params as they come in. Another design could have been creating a temporary user at each step with a mixed-in ActiveModel::Validator class that represents the current step. I used erb as my templating engine due to time constraints and familiarity. Thank you so much for taking the time to review, and for your consideration!
bundlerake db:migrate
rake