LOL. hope they're really big screws.
I realised Brad never made it to your topic. For dab spacing I can remember in several of his videos he references 'watching the reflection of the tungsten in the puddle. I've been working on it during my practice time and i still have a long way to go. I think i remember that he said he aims for 1/2-1/3 overlap on each "dime". Roy has a great fideo on where to look that helped me with keeping the toes lined up.
Aluminum allows for the larger stepover as far as bead spacing is concerned. Mild steel makes for a relatively narrower bead and smaller "dimes" but the overlap translates fine. Stainless of course is a drag race to beat the heat, but again, same stepover relationship.
The overall appearance is up to you.
I do some drills to improve my consistency...Maybe they'll kick in one of these days lol.
-Scribe out some 1" lines and 2" lines.(length not important-just need to be the same.)
Count out your dabs for a couple 1" welds.
Now Do all the 1" welds with the same number of dabs.
Now double it for twice the length.
So on and so forth.