Getting two pieces to join can be a little tricky. The good news is once you get that first tack, it's a lot easier to keep things going. The trick is to have both pieces super clean and fitted closely. Then start with a low amperage and let the cleaning action work, moving the arc from one part to the other. This will also build some heat into both parts. Then crank up the amperage to start a puddle, and add some filler. Work the arc to wash that puddle over to the other part. Remember molten metal will flow towards the heat source, and arc force can also push it around. Sometimes a quick blast at higher amperage will do the trick for you.
You can use thoriated or ceriated as well. Be sure to keep your AC balance below 40% to keep your tungsten in good shape.
Not sure what is going on with your stubby kit. Is everything sealed up good? 20 cfh is about all you want to run, you can usually get by with less depending on cup size. 10-15 cfh is a good place to start.
Cup size depends on amperage and the material you are welding. Aluminum needs a larger cup than steel, stainless larger yet, and titanium requires a giant one.
For thin sheet metal work a 1/16" tungsten and a #4 cup is a good combo for steel. Moving to your 1/8" aluminum, bump that to 3/32" tungsten and a #6 - #8 cup.
The amount of amperage required depends on a number of factors. With small parts of aluminum, you will find you need less and less as the part heats up.
With a lap joint, the thing to do is build the weld from the lower part, first. Edges melt much easier, and corners easier still, so don't start there if possible.
Long arc, short arc, heliarc and in-the-dark!