In anticipation of using scrcpy (Android Screen Casting) on Linux and installing EasyTether for Android I have enabled “Developer options”.
“Developer options” needs to be enabled in order to enable “USB debugging” which is required for both applications. For further information you can look at the following pages.
Sure it can, why not? Having Developer Options enabled, you can even use adb install F-Droid.apk after having downloaded the APK to your computer. And before you ask: yes, you can also install other apps (e.g. with the F-Droid app) while developer options are enabled. I do that all the time
Actually, removing all the Google apps that shipped with your device is a thing almost impossible to achieve. If you really want to go completely Google-free, the way to go is a custom ROM – but I doubt there is one for a device that unknown (I might be wrong here, though). So the closest you can get to it is uninstalling what you can (and don’t need), disabling the rest you don’t need, and that’s it. You’ll still be left with the Google Play Services, and some other apps, unfortunately.
As for the order: As long as you don’t start over with a custom ROM, it’s as Licaon_Kter just wrote: doesn’t really matter. I’d start with our app and see step by step which of the non-free apps you can replace by free apps from here.