How to switch to Fido

So I’m currently on a $42 20gb virgin mobile plan. I want to switch to the Black Friday $34 60gb plan fido is offering but I’m a bit confused how it all works.

So I choose the plan online, tell them to port my old number, then will my current virgin mobile plan still work while my sim card comes in? What’s the point of the temporary number? I’m concerned about the disruption to my service. Also is there a way to avoid the $25 sim card shipping fee, cause if Virgin offers a win back then I’d have paid that for nothing