You can set up your apache/nginx or whatever webserver to redirect http requests to https. That way you can still link to your website with an http:// URL.
Appreciated, but this is a hacky solution. If you use the graph explorer, both the http and https addresses have different counts. It's very frustrating - shouldn't be that way.
True. And you have to be extra careful with HSTS Preloading; if one of your subdomains breaks because of HTTPS, it'll be a pain to get your domain taken off the list.