> You need multiple physical links in running to different ISPs because builders working on properties further down the street could accidentally cut through your fibre.

At my last job we provided redundant paths (including entry to your building) as an add-on service. So you might not need two ISPs if you're only worried about fiber cuts. You could still be worried about things like "we think all Juniper routers in the world will die at the exact same instant", in which case you need to make sure you pick an ISP that uses Cisco equipment. And of course, it's possible that your ISP pushes a bad route and breaks the entirety of their link to the rest of the Internet.