Want to get XFINITY mobile but I am not "primary user"

I want to switch to XFINITY MOBILE plan but I am only an authorized user on my household's xfinity account. If I want to be able to order and manage my XFINITY MOBILE plan do I need to have my roommate do a 'billing transfer responsibility' OR does he simply need to make my account the primary rather than 'user' only?

Also can I port my number and then within 30 days if I decide to upgrade to the iPhone be elegible for the $250 cashback (not leasing the device, will buy outright) thanks!