Yes, you would purchase the Mofi router separately. Not necessary unless you need multiple internet connections at the same time ie. streaming video while surfing the internet or multiple users on the connection (team drivers).
Visible will let you bring your own phone IF it’s compatible with their network. There’s a tool to check if your phone’s compatible on their website. If you don’t have a compatible phone you would have to buy one from them. Cheapest option is $79 right now.