I also noticed an outages-announce - is that for people who don't sub to
the other two, or should one do all 3 to be fully notified?



No, that's for changes and updates related to the list. I would stick with w/ outages@ and outages-discussion@ as mentioned below.

outages@outages.org - Warnings of (un)planned outages and reports of observed current outages
outages-discussion@outages.org - Discussion about post outages (troubleshooting, analysis, post-mortem, venting, etc).
outages-announce@outages.org - Change management and future updates related to the lists.