the best way is to use 2times the kicad-manager, with 2 different projects.
If you want to look at the same project/schematic just copy the project-directory into another folder
you can also use eeschema/pcbnew as standalone-programs. So you don’t have to open a complete project but only a desired schematic.
you can also use 2times kicad on the same project/schematic. Kicad will detect this and warn you about “already open files”. As long as you don’t save the second instance this could work and could be used for instance to show different areas of the same schematic/board. But you should know what you do and I would recommend only for experienced users.
I’m running Kicad 6.99 on a Windows 10 PC
Your questions 1…4 sound as if you are new to Kicad. For new users I would recommend the actual stable Kicad-version v6.0.2 (as of 21.02.2022). The v6.99 are the nightly development version and is currently not 100% stable. (for instance the last 3 days the drc led to a crash).