Welding questions

It's not 30 gauge wire, it's 0.030'' wire which is actually a little too big for welding sheet metal unless you are quite skilled.
I would suggest changing to a 0.024 sized wire and your voltage at a lower setting like 2 out of 4 and the wire speed at 50 to 70. The wire stickout from the tip should be 1/4'' max and your gas should be around 25 cfm.
These are just basic settings, but should get you in the ball park for welding sheet metal. Your choice for shielding gas is right on.
Remember, the voltage is penetration and the wire speed is heat.
Do not run a continuous bead, do it in steps for sheet metal or it will warp badly, especially on a big flat surface. Heat is your enemy!
What I do is a series of tacks that are spaced out over the joint evenly, and take your time to let it cool or use a air chuck to blow cold air where you just welded to cool it off quicker.
It takes a lot of time and patience, but it is very satisfying.
Practise on some scrap before you start on the real deal.
There are lots of videos and info on the net, I suggest you look some up, and there is some pictures in my build thread too if you care to look.
Good luck.