Some questions and concerns:
-Generating a group manually with an arbitrary group ID, instead of using the groupadd command, which will make sure that the ID created is the correct number and there are no clashes with existing groups. Why did you go with manually generating the group ID?
-Allowing write access for the device to all with the dreaded 0666. This is asking for trouble on many levels. Can the permissions be reduced to 0640, with what you have assembled?