1 I assume that means that anyone using AutoUpdate will get it automatically.

That's not necessarily correct.  If you have the "give me recommended updates the same way I receive important updates" box unchecked, Windows won't automatically d/l them (assuming you have Important updates installed automatically).

I actually have about 30 recommended updates in queue, waiting for me to approve them... including the W10 install thingy.

2 I've done four Windows 10 installs now - two old notebooks I was handing down to my nephews, one new notebook, and a virtual machine on my Mac.

Windows 10 itself is good enough, as long as you turn off every single option it offers during the install process.  (There's three full screens of helpful things Microsoft offer you, and you want none of them.)  Installing a clean copy is easy and very quick.  I know my iMac is supposed to be fast, but watching Windows install itself in under a minute was a new experience.

The process for upgrading an existing machine is...    Fraught.  Don't let the automated download do its thing; it will very likely break.  (It hasn't worked even once for me.)  It won't break your machine, but it won't upgrade you to Windows 10.

Instead, download the ISO from Microsoft and use their install tool to load it from a thumb drive.  That approach is mostly painless.

Or, of course, just stick with Windows 7.

3 Sticking with earlier versions of Windows might not be a choice much longer. Botnets can become a matter of national security, and Microsoft is "too big to fail," let alone be taken down for refusing to keep earlier OSes patched and secure.
I'm going to move all the "stuff that could get me in trouble" to cold storage, do the upgrade, and see if I can set up a dual-boot with Windows 10 (for video games) and Linux (for everything else). Just gotta remember to never install a real web browser or video viewer in Windows again, I've already trained myself to always cancel whenever anything opens an IE or Windows Media Player window.