The harsh hit can be caused by a few different things. Usually it's a combination of juice (nicotine strength, higher PG/VG ratio, other "irritant" components). Another component is the power output - determined by voltage and resistance. In short, decreasing nicotine level, decreasing the PG and increasing the Ohms will result in a lower throat hit.
That said, in this case it could also be how well you feed your atomizer with juice. If the harsh hit is intermittent, that this could be because you vape a dry atty, and you need to feed it more (sqwonk longer, make sure you tip the mod when you sqwonk as, as far as I know, this doesn't have a tube going into the bottle itself).
For the other question, the VMod version 2 takes almost anything you can fit on a 510 connection - 510 and 305 atomizers (make sure they are not the sealed bottom type) and pretty much any 510 cartomizer. It comes with a little adapter in there that allows you to connect them. Some "thicker" attachments might not fit well.
I don't own one, but I was researching to buy it myself at some point - hence, someone who has it might give better answers.