It doesn’t matter which class you choose first, especially at 11 level, since you can respec all points, including Mastery points, freely. You cannot only respec classes.
Btw these 2 builds you found are considered melee that’s why I didn’t recommend you such, you asked for a mage in the title.
Here are some more beginner guides / leveling: Beginner build guides Compendium (for AoM + FG expansions)