UPS Advice I wish I had gotten
Nobody told me -
Don't follow the standard instructions and add up the power of all your critical computers and devices and find the largest UPS that can handle them.
If you have multiple Macs (or other computers) and they are in the same location (room or home office area), buy smaller separate UPS for each one if you want the simplicity of using auto-shutdown with a USB cable sensor from the UPS.
None of the consumer/retail UPS systems can notify multiple computers, so only one of your computers will get a shutdown signal. You will have to resort to hacks and workarounds that for me are not reliable enough and worth the hassle.
On a related note, think carefully about wanting your network (especially Wi-Fi) to stay up for a while during a power failure. With modern networks possibly having separate cable modem, router, access point, firewall there are potentially a lot of little boxes that all need to stay up.
Mesh Wi-Fi means you may have access points and extra Ethernet switches or PoE power supplies scattered around your home that one tends to overlook when doing UPS power planning too!