To answer your question, I have a total of 73 windows open at the moment. 11 of them are from applications with a single window open, 8 are from iTerm, and 54 are from Sublime Text. I am aware that is quite a lot for Sublime, but that is just how I use it.
Regardless, I just quit Sublime Text, and the memory usage only dropped to 8.9GB still absurdly high for having 19 windows open.
WindowServer has consistently been the main culprit but occasionally other apps like to chip in where they can too. Often that means there isn’t one single process which I can kill to reclaim enough memory to continue working without being promoted again or having MacOS forcibly close all my applications on me. As a result, reboots appear to be the only real solution for me.
Interestingly though, in the past few weeks I have been working with similar numbers of open Sublime Text windows as yourself and I can confirm that since then, ST4 has been a regular and serious offender when it comes to memory usage in Activity Monitor.
https://gist.github.com/ccampbell/9a0118b0e3e607ec56a3a2cc59...