Hi Sysadmin_D,
1) If this dropped in your lap, how would YOU start (or suggest I start)?
--> Install SEPM on test machine with the help of following article
https://www-secure.symantec.com/connect/articles/sep-121-fresh-installation-graphical-overview
Navigate through SEPM main tabs i.e. Home, Monitor, Reports,Policies, Clients & Admin tabs.
For queries you can place search here http://www.symantec.com/business/support/index?page=landing&key=54619 & SEP forum is always there to help you.
At SEP forum we have many article's & video's are available
https://www-secure.symantec.com/connect/security/articles
https://www-secure.symantec.com/connect/security/videos
2) How do you reconcile the numerical version numbers to their equivalent RU/MP designations? Is there a table somewhere that can be linked to for future reference?
--> Check till date releases at http://bit.ly/m0vOJp
3) Best Practices suggest I upgrade to latest 11.x release before upgrading, but I think the supported upgrade paths require 2 updates anyway. So, should I update 11.6->11.7->12.1 RU1, or 11.6->12.1->12.1 RU1 (I think those paths are correct)?
--> No, you would required one upgrade only
If you are using RU6 then upgrade path is RU6 --> SEP 12.1 RU1
4) Our SEPM server is virtualized in VMware, so I can snapshot before the upgrade and revert if something goes awry. Are there any gotchas here that you know of? DO I still need to backup the local DB?
--> Yes, you can revert back with Snapshot, but it's always recommended to keep DB backup at safe place for disaster recovery. I used to follow onsite backup and offsite backup concept.
Now, to learn upgrade process please check this article
SEP 11.x to SEP 12.1 Upgrade process graphical overview
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
I hope it will help you.