No lie, the new owner flex sealed the entire underside of the dishwasher! 

Bought appliances for $1500 but the kitchen sits unfinished, the bathroom is gutted, a back room was cleaned up to make more living space but won't work well unless its insulated from the underside and its now yucky winter and Ill pay through the nose to have someone go under there.

I personally prefer to pull the nails all the way through, out the underside of the wood, to prevent splitting.

Might not be the sort of job you want to do your self, but if you have access to the underside of the floor you can at least see what's going on.

N1102.2.8 (R402.2.8) Floors Floor framing-cavity insulation shall be installed to maintain permanent contact with the underside of the subfloor decking.

Window is currently not egress, but can certainly be replaced if needed.There is a walkout door right next to the window, so I’d imagine, that is what is necessary for an emergency.Front side of basement has another window (same size as back), and has a view to the underside of the porch.

If I were doing this, I would definitely go with an air-impermeable spray foam -- sprayed tight to the underside of the roof sheathing to the thickness required to get the code R-value. 

The most common scenario if you don't remedy the situation is that you would have to replace that portion of the roof sooner and that some of the roof decking will have dry rotted from the condensation forming on the underside over time.

Did you apply closed/open cell spray foam - or strap and use packed cellulose/hemp/fibre - the outer walls and underside of the roof deck (requiring an over roof) or did you maintain ventilation under the roof-deck and insulate over your ceiling?

The other is to not add any insul to the other under side and leave it be.