You can hide/show sections of an Adaptive Form depending upon the values of other Fields using the visibility expression in the edit dialogs of the section. You can input a data xml to prepopulate the form as described in 
Thank you, the linked post is helpful.
Within an adaptive form, is it possible to show/hide some of the sections based on server logic. For example, some templates using a wizard-style interface and I would want to be able to select which sections to show, hiding ones I may not need.
Also, how would I pre-populate data into a new form?
Adaptive Form Fragment support in not yet available but is on our road map. Till that is available, you can create composite components and use that as reusable collection of fields as mentioned here.