It wouldn't be a bad idea to run your first pass, in the groove, with a 1/8" 6010 or 6011 to get the most penetration and then fill it up with 7018. Nothing wrong with using a grinder to completely clean out all the slag from the previous pass. Also make sure to clean the sides of the welds to make sure you have good fusion at the edge. 1/8" 6010/11 will run around 100/110 amps and 1/8" 7018 around 130 amps but you can't go buy the dial on the machine. Get some scrap pieces and if at all possible, grind a similar V to practice on. DC is way better than AC. Electricity, at least referring to DC on a welder, flows from negative to positive. That's why hooking the stinger on the - is referred to as straight polarity and on the + is referred to as reverse polarity. One of the things they tell you to remember in school is DCRP=EP, Direct current Reverse Polarity equals Electrode Positive. 6010 runs DCRP but just to see the difference, try it on DC straight polarity or AC. 6010 is known as a polarity check rod.