1) Nope, that's specifically for browser debugging so you don't need it. If you look in older versions of Flash these files are in the Player folder. I imagine Flash executed them as needed (named InstallAX.exe and InstallPlugin.exe). You can omit that step if you like. It doesn't hurt however. If a newer "non-debug" version comes out you will still be prompted to update Flash so you won't miss anything.
2) Correct, that is just a Flash Player. Again since the older days this file was always told to be replaced with the latest player. I assumed Flash was using this Release\FlashPlayer.exe when perhaps you made a projector and it needed to embed Flash Player inside it. I've kept it in my update workflow for years.
The \Debug\FlashPlayerDebugger.exe is a different story. This is the file you need to replace to debug using the latest debugger. This is executed when you hit CTRL+SHIFT+ENTER. So you want file number 3 (oddly named Projector content debugger (for Netscape-compatible browsers)). The name confusingly infers it is a Projector but also for browsers, but it's the debugger. Rename this file FlashPlayerDebugger.exe and overwrite your existing FlashPlayerDebugger.exe in the Players\Debug\ folder.
Make sure you restart Flash if it was running while you made any changes and try the debugger.