14 Gauge tubing is about .072”-.085” thickness, so a 3/32” stick electrode is *just a little too large* IMO. You could measure the thickness of your tubing; a 3/32” on .085” is probably fine, but I wouldn’t use a 3/32” on .072”.
You can easily find 1/16” 6013, but 6013 only has medium penetration at best, & the 1/16” stick electrodes sure do move around a lot (i.e. they are not very rigid).
Personally, I don’t think much of 6013. It runs beautifully, but medium penetration is not good enough.
You can find 1/16” 7014. I have stick welded a fair amount of .050” wall tubing with 1/16” 7014 (which was just practice that I was doing to challenge myself). I am not a huge fan of 7014. It runs okay, but the penetration is just a little hotter than medium.
As far as preheating the rods: with 7018 or any other low hydrogen stick electrode, I will preheat in a rod oven (about 245°F) if the new, sealed canister or other packaging was opened less than 4-5 hours prior to welding.
Preheating the workpiece will help with the arc initiation. If you don’t preheat (as I don’t) the stick electrode will strike easier once you have welded on it enough to heat up the workpiece. If you get frustrated on a restart, just grab a new electrode (as opposed to a partially used electrode).
I (1) look at the packaging for the amperage range, (2) Google it, or (3) figure 1A per .001” of material thickness.
I would definitely practice on scrap before working on the workpiece!
I do all of my stick welding with 6010 and/or 7018, & always DCEP.
The recommendation of 160A on 14 gauge material is more than double the recommended amperage. Again, I am definitely looking at the packaging for the amperage range.