New windows/stone siding

We recently purchased a home built in the early 1950's with an addition put on in the 80's. We're hoping to remove the vinyl siding and replace it with some kind of stone and increase the insulation next year, but in the meantime we want to replace the original windows (some wooden sash from the 50's and some aluminum sliders from the 80's) in our childrens bedrooms before winter.

We'll likely hire a carpenter to do the job, but I'm wondering what considerations need to be taken to ensure that the exterior work next year won't be odd looking, difficult or more expensive than necessary.