Michael,
The following line:
%sudo ALL=(ALL) NOPASSWD: ALL
literally means:
ALL users in the sudo group can execute ALL commands as ALL users from ALL places without a password.
Without any lines after this. The only thing that you would need to do is add users to the sudo group (/etc/group). Thus the line:
$ sudo useradd -G sudo <user>
The %sudo portion of the stanza tells Linux to look in the /etc/group file for a line starting with "sudo" and include any users listed on that line in the sudo group. This way you don't have to add them individually as separate lines in the sudoers file. For example lets say you have 3 users (john, jane, sam) that you want to have sudo rights w/o a password. It could be done in one of two ways:
1st- in sudoers
jane ALL=(ALL) NOPASSWD: ALL
john ALL=(ALL) NOPASSWD: ALL
sam ALL=(ALL) NOPASSWD: ALL
or
2nd - in sudoers and /etc/group
%sudo ALL=(ALL) NOPASSWD: ALL
in /etc/group
sudo:x:##:john,jane,sam
Both work but programmatically the 2nd option eliminates redundant code when writing scripts and allows the use of additional shell commands (and arguably more simple ones) to be used to maintain file changes (i.e. sudo useradd -a -G sudo <user>). When scripting it is easier add the use of usermod and useradd to a script than to use commands like sed -i and then having to escape special characters like "%, (, and )" when making changes or updates.