Excellent advice. Especially on the mainspring. So many people want to replace and/or modify it for a "cool" hair trigger, just to end up with too light strikes.
I would add though that, sometimes the burrs are not easy to find. The ones that mark the frame/faceplate are easy enough. I got a 1500 grit stone, that I broke the end of to get some smaller pieces.
Then I took it to basically all the inner contact points. My old 27-2 went from 4 pound single action and 8 pound double to 2 and 5 just with polishing and getting a 13pound Wolffs rebound spring. Did not touch the mainspring or the single action hammer sear.
Doc