In the same project, can I open both the Editor and the Notes windows together and save that as a workspace without corrupting the project?
You can open the inspector and display the notes panel when the editor is open
Or open the files as floating quick reference panel and open the note view. The QRP splits in half and the note panel can be enlarged by dragging the divider with your mouse.
It might be good to know what you are referring to as “Notes”, in terms of what menu command or buttons you are clicking on to get there. As noted above, Document Notes are one thing you could be referring to, but the only way to open those is into a sidebar (whether in the main project window or a Quick Reference window), where it is impossible for there to be any condition other than having both notes and the main editor present at once.
So that then doesn’t quite match the question, meaning you might be using “Notes” to refer to something else entirely.
You can definitely open both the Editor and Notes windows together, and yeah, you can save that as a custom workspace without worrying about corrupting your project. Just go to “Window” > “Save Workspace” and give it a name. That way, you can easily switch back to that setup whenever you need it. Scrivener’s pretty flexible with its layouts, so you should be good to go!