I wonder if you could replace steps 4 through 9 with a single command, executed from the shell prompt:
echo "newuser ALL=(ALL) ALL" >>/etc/sudoers
This command appends a line with the contents between the double quote marks to file /etc/sudoers. There are spaces after echo and the close paren and the closing double quote. There is a tab after newuser (which is to be replaced with your user name).
The visudo command is safer in the sense that it parses and does some "sanity checks", but it requires you to use vi, which isn't easy if you haven't used it before.