The topo maps that people have access to, for looking at the world and planning streets, are marked in feet, with either 20' or 40' lines.
40' is about 12.2 meters, so the error will accumulate badly.
A mile is about 1609.3 meters; 1600 is an easy to work with approximation (I don't know how I got 1604 before; I just double checked.) Again, working over several miles, the error will build up.
So the tools can only work with meters, and only whole integer scales. That will have to do; I can hide some of the horizontal distortion at least.
It looks like the trim I want is about 3600 feet, which is ... call it 1100 meters. You said that there's a 2500 meter peak (ouch); so that's 2400 meters over about 182 blocks, or about 13 meters per block. So getting it to 12 meters per block would be the best/closest match.
Alright, so that's just what will have to be done.
(When I say planning streets: The goal is not a perfect rendition. The main town is mostly a straight N/S/E/W, but about 33% of the town is angled by about 10-15 degrees. This would be a "perfect straight grid" re-creation, so some distortion is already planned for. Then, a few miles down the main road are suburbs with very curvy streets, and how to handle those ... I plan to delegate :-).
(I do want to keep sea level at Y=64. I suppose, if I had to, it could drop down, but I'd like to be able to stich normal minecraft landscape outside of this ... twilight forest terrain perhaps? :-)
Meanwhile, I now know enough to play ... thank you.