0) yes or yes. You can do both
1) yes
2) yes if they are the ones for your gps
3) definitively 100% safe. The warning is just because more features are enabled on Asian firmware
4) I always use the .rgn flash method using updater.exe. For the .GCD method to work, you hve to change the SW Version or the gps will not flash it. For example, if you have v 4.70, change it to 4.71. If you need more flashing, you can change it to 4.72 or go back to 4.70.