I run a website about this kind of thing. You might find this page useful: https://startyourownisp.com/posts/backhaul-picker/

Nice, this is exactly the kind of practical guide and reference material I was looking for!

There are open comprehensive resources like the open book "WiFi networking in the developing world" [1] which seem pertinent here even though we're talking about North America. :P

[1]: http://wndw.net/book.html

Also very curious also. At ~12km I would think it would require some specialized microwave testing equipment to get the alignment right.

12km isn't too bad actually for alignment unless you're using really high frequency (>10Ghz) equipment. Even then though you probably don't need specialized equipment other than maybe binoculars and a voltmeter[1]. I've taught beginners to align 24ghz radios at 12km by hand.

[1]The voltmeter is for quick feedback on the signal level as you aim. Many high-capacity wireless radios have a connection point on the back that will adjust voltage to match the current receive signal level (measured in dBm). That's usually the fastest way to watch the signal level as you aim, especially if you're hanging off a tower while you do it.