Check into whatever 3D printed Gemini Spacecraft there may be. Get it resized to match the scale you want, if it's not too crazy expensive.
The old original Estes Gemini capsule out of balsa was a PITA to cut out the window areas correctly. If the windows are not done right, it makes the whole model sorta suck. And yeah, as a kid I had one, and yeah, the capsule I made sucked.
Even today, if I was tasked with making a GOOD one using that balsa capsule (not allowed to do 3D print), I'd get several balsa ones to butcher and learn with, do them all, and pick the best (least bad) one. One thing for example, the "flat" part of the windows are not parallel to the base of the spacecraft, they are slanted. But the biggest PITA is that rounded concave area in front of the widows. And trying to get them look identical. "Right one is too small, cut/sand some more. Oops, now it's too big, so widen the left one. Oops now the shapes are mismatched...AGAIN."
I have seen some people post photos of models of Gemini-Titans they took great pride in. But the windows were not so great or even sucked. I didn't comment on those though, since the builders were happy enough with the result. There was no useful reason to point that out unless they asked for comments on how it looked scale-wise or improving for the next one they might build.
So, anyway, unless you have great skills up to the task of doing those windows well, that's why I highly recommend a 3D printed spacecraft.
In this case, part of my skill is recognizing areas I'm weak in that I need to figure out an alternative way to do it, or elect not to build that and go with something else. Not suggesting you avoid building it, go for what interests you to build! Just that's one reason why my first butchered Gemini-Titan remains my last. I appreciate the rocket, but even when Estes did sell the 1980's version with plastic spacecraft, I didn't bother to get one (wish I had, though). Oddly enough, I have had 1/100 Saturn-V kits..... but never built any (got them mostly as collectors items and sold most long ago). I did build the ancient 1/242 scale (BT-60) semi-scale model, and man did THAT suck (in the hobby less than a year, and not the easiest kit to build well. Had a Centuri 1/100 Little Joe-II and that DID turn out pretty well since it was more builder-friendly to do a decent job with, plastic parts and wraps for the body/fins)
