Great feedback, and a very well-written summary. My plan is to do a complete teardown and properly lubricate everything as you suggested before breaking out the stones.
I did a field strip of the gun after my first trip to the range and added some gun oil to exposed parts. After letting the oil soak in overnight, the trigger was already behaving much better.
For all I know, this gun hasn't been fired (or fired much) in over 50 years, although it has been well cared for (the finish is perfect with no pitting anywhere -- looks like the gun was made yesterday).
I think I'll start with the simple stuff (complete breakdown, oiling, and greasing of the rails) and then spend some "quality time" with the Double Action trigger and some 9x18 Makarov Snap Caps. Then I'll report back in a week or two.