I don't notice much of a problem from multiple windows. I sometimes have a dozen going.

It's the language extensions in the windows that can cause me problems e.g. rust-analyzer is currently using more than 10GB! If windows are just for reading code and I'm feeling some memory pressure then I kill the language server / disable the extension for that window.

I have more problems with jetbrains. 64GB isn't enough for a dev machine to work on 10s of Mbs of code any more...