Originally Posted by swindmill
What I'm not 100% sure of is how to know if a certain receptacle is a good source of power. If I have an outlet with live/neutral/ground connected, can I simply run new 12/2 from the unused connections on that receptacle? Alternatively (maybe better), there is an outlet in the BR near where the attic is that I will never use. Can I remove that outlet and use that wire as a source?
You could get a clamp-on ammeter
and measure the typical current through the breakers in your panel that are handled by your candidate outlets.
Pick an outlet served by a breaker that typically runs well below it's rated 15A or 20A capacity.
If an outlet can run a hair dryer at full speed and full power, the wiring connection integrity is good all the way back to the panel.