Is it possible to show/hide pages within a form based on if a checkbox is selected or not?

Yes you can, by using the Panel control.

Place other controls inside the panel and then apply a Validation rule to that panel to hide it when your condition is not met.

You can also use Choice Control, set it to Render as Buttons and that way you can create tabs on your form for multiple pages.

It's very simple to do and there's a few articles that involve some CSS to "jazz" it up a bit. Even an Xchange resource.

CREATING TABBED FORMS IN NINTEX FORMS FOR OFFICE 365 

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Thanks