Crawlspace insulation

I think an attic ventilation system will definitely help with your problems. Fortunately, you can also sort of step up with ventilation as you go, adding powered fans if the vents you put in at first dont work as well as you'd expect.

In the winter, having a properly vented attic will help prevent ice dams in gutters, and can help with heat problems in the summer too. In your attic (above the insulation) should ideally be close to the same temperature as the outside. It should be cold in the winter, and hot in the summer.

For the ventilation, you should have some soffit vents on the bottom and a vent on the side (near the top) or on the top (like a ridge-line vent). That will allow the air to move freely.

If the air doesn't move as well as you'd like, you can wire in an attic fan to help push the air along.

I am also in the Northeast and have had to tackle this type of situation a few times. There are several ways to attack it.

In your case, the best solution, but unfortunately the most expensive would be to use an open cell foam kit to fill the joist bays. They are fairly easy to use and give you about an R-4 rating per inch. They are a two tank kit with a hose and wand. Here is an example product: Touch N Seal 1000 Kit Open Cell Spray Foam Insulation

These type of kits start around $400, depending on the square footage and depth required.

A cheaper method would be to use 24 inch R-19 unfaced blanket insulation cut to your custom widths. You can use wire springs to hold it in place and keep it from falling. I would then cover the entire area with 4 to 6 mil plastic, stapled to all the joists. Tape the joints, if any. Moisture should not be a major problem since you have already done what sounds like a good job sealing the dirt floor. In the summer months, some ventilation in the crawl space will also help avoid excess moisture.

Rigid foam glued to the foundation walls would also help if the area is fairly air tight. If there is free air flow, insulating the brick walls would be a waste of time and money.