We are doing the exact same thing in our remodel as we speak. The question is whether or not the window is getting wider as well and not just shorter.

Our windows will retain the same width but will decrease in height.

If only decreasing the height, the order would be:
1) Remove existing interior trim and window.
2) Reframe the window to correct size.
3) Install new window.
4) Cover the exterior side of framing with plywood.
5) Install insulation in new framing.
6) Cover the interior portion with drywall (wouldn't necessarily have to finish the drywall if it's behind cabinets).
7) Exterior brickwork.

That being said, you could do everything except the brickwork and be fine until spring.

I should have also said that you'd be fine until spring if you make the exposed plywood waterproof/moisture proof (caulking, covering, etc.)

That's great thank you for the detailed explanation

Make sure you flash thevwindow properly for your application too.