New Phone, New Phone Number Needed.

I’m gifting my son his first cell. I have purchased a non Koodo refurb, unlocked (first gen iphone se). I’m adding him to my account with a plan, and I know i need a sim but how do i get a phone number? I can’t seem to find an answer to this, only how to port numbers. 
I’m trying to do this online to save $40,  I’ve added the sim and selected a plan, and am at the “Permissions”  in the checkout. I’m assuming that I should select “Someone with authority has to make purchases on the account” , meaning if my son over runs the data, he can’t top it up? And can’t access any other add ons without my permission?  Correct? 

Under the help for this it reads:

“For numbers without authority, they''ll need to contact somebody with authority to make any changes by logging into Self Serve. Tip: avoid providing Self Serve access to numbers without authority.”

But how do i get a new number for this phone I’m gifting my son, over which he will have no authority? :)
Is that step to follow? Is that the “Add Line” at the bottom? Nothing happens when I click on it.

What i’m trying to achieve - an unlocked BYOD that needs a new phone number, a sim, and a new plan on my account. The new phone number is unclear in this process.

Thanx in advance.