That sounds correct, but you would want to remove interior trim and check the rough opening in a few spots. (Or pop off exterior trim if you have any) If your new window fin sits inside the edges of the stucco you should be able to fill the void with trim, seal edges with a good polyurethane caulk. (Don't know if you have table saw etc to do that) You could clad with aluminum trim coil if you want. (Would probably need to hire it done if you don't have access to a brake) If you know a good stucco guy that's an option but really that's only necessary if you want your window trim to be one standard size on the entire house... or if you don't want trim at all. So I guess if you want to try to do it all yourself, I would say filling in with exterior trim, caulking and painting would be your best option. Stucco guys don't always get the texture right, and really, they should carefully hammer a larger perimeter (rough random edge) out around their patch... while preserving the paper and wire lath, and add new paper and wire lath as needed. The you'd need to caulk the repaired stucco to the window after it has had time to cure.

Your response appears to confirm that a good quality, vented fiberglass door painted white or another light color should be OK with some late day sun exposure in NY. A stained medium or dark fiberglass door behind a full glass unvented storm door and exposed to the sun is asking for trouble. Unless anyone argues otherwise, consider the plan for our fiberglass door to have low risk of resulting in sun damage. THX

Make sure you order it storm door ready so that the stiles/mullions, if sidelights are built up to allow for the installation of a storm door. Having lived in both Upstate New York and Southeast Virginia. Upstate never approaches the heat extremes that we face down in Virginia. Keep the color scheme light, ThermaTru is an excellent door. I have never had problems down here with that brand.