The Historic District

Whatever it's painted with has been trapping moisture, the degradation is just the visible result.

I, too, learned sash joinery from Roy Underhill's program. I have a molding cutter for the newer ogee sticking profile, and two "sash ovalo" molding planes for the earlier types.
Casey

Use oxalic acid solution (mixed by dissolving the crystals in boiling hot water) to take out iron stains from marble.

Places I don't paint or anything: sides and top of top sash. Sides of bottom sash. Top half of the parting bead. Top half of the upper sash race/channel (unless it was primed originally). Use oil paint. If you can manage it, finish-paint the sash and jamb before re-installing the sash. Paint careful...

What a find! Good eye.
Casey

I'm no legal eagle,but aren't you supposed to give your neighbor the "pretty side" of a fence so as not to degrade his property value with your fence?

Don't bend the molding, the eye will see the crooked line. Your idea to float the ceiling down is right. IMO you don't need any wire, structolite will adhere to oil primer (let it cure, though!), use a straigtedge to get it flat, topcoat with easysand and green-lid mud.
https://www.wind-lock.com/drywall-darbies/
Casey

Heat the female threaded piece with a MAPP gas torch, apply ice to the male piece, use vice-grips.

I can't tell you how many hundreds of push-points I have cut down with nippers or shears. One summer I glazed over 500 panes, so that should give you some idea.
Casey

I just push mine home with a putty knife. I quite favor using the modern style point that most on here hate, I just trim them in length with a pair of snips so they dont stick up too far (their biggest, perhaps only downside) You said it, Mick...I favor the diamonds, myself. I feel they offer more ...