Have you ever been on a plane before?
100 square inches is a reasonable approximation from itchy, here are some specs I found by Googling:
The dimensions for (most of) the 707, 727, and 737 airplanes are 10"x14". This isn't specific to your question, but the original spec. for the 707 and 720 windows was 9"x12.5" (this is per a TWA station diagram from a maintenance manual I have that lists their 707 windows as, and I quote: "9x12.5 (typ.)"). IIRC only American ordered their 707s and 720s with the now-standard larger panes, but the 707 is a different beast altogether; regardless, once the 727 came along, the 10"x14" standard was pretty well set in stone...
Back to your question, though: Even the newest 737s are still 10"x14", though they look different most certainly from the inside and to a lesser extent from the outside, as the "Sky" interior uses cabin wall panels that cover portions of the windows to give the illusion of being closer to what's on the 787, which can be more or less visible, depending on your viewing angle.
Also of note if you're drawing your own windows: The corner radii for all cabin windows--including the earlier smaller early 707/720 versions--are 3".
Spacing is nominally 20" on center, which matches Boeing's standard fuselage frame spacing: But watch out, as on the 737 the frame interval aft of the overwing exits varies, albeit quite slightly. It's not really noticeable until you see it the first time...And then, if you're like me, you'll never be able to *stop* seeing the difference
There are other spacing peculiarities based on variant (which won't matter to you since you're not building a long-body airplane), as some are slightly moved and/or missing altogether due to placement of internal components (mostly ventilation duct risers, bulkheads, lavatories, etc.; a duct riser is the reason for the missing window that first showed up on the 737-300).