People smoke differently and they also vape differently - from how they inhale and so one as well as how they react to flavors themselves, the nicotine and the type/amount of glycerin/glycol.
When it comes to something like a dry throat/sore throat consider that nicotine dehydrates mucus membranes so the lower the mgs of nicotine you the less the dehydrating effect. Increasing your water consumption will do the most good. Your throat will become more used to and more resistant to the drying effected after a while, but you could consider a throat spray or cough drop to help in the meantime.
Throat hit from the vapor is also related to the strength of the nicotine you vape. If you find its harder then you like or makes your throat/esophagus sore then you need to consider a low mgs.
As for PG/VG they are more directly related to vapor production and don't really have an effect in the way nicotine does. That said, some people find that PG is not always agreeable to them so if your are sensitive to PG you might want to consider a PG/VG mix. The quickest way to find out if you are more sensitive to PG then most is to try a flavor made with 50 to 100 % VG (vegetable glycerin) and see if that eases your throat. If that solves the problem you can just continue on the per cent you tried or try some other percent mixes ( 20/80, 30/70, 70/30 and so on) for which gives you the best experience.
What is not true is that the number of mgs of nicotine is not necessarily a 1 to 1 correlation with how many cigarettes or pack of cigarettes they used to smoke. Since people smoke differently there are people that smoke as many puffs as possible and inhale every bit of smoke and would definitely be getting a higher level of nicotine in their blood then someone who lets a lot burn to ash, only hits about half the cigarette and does not inhale deeply every time. They can both smoke the same brand cigarette, and the same number and the first will have a higher blood nicotine level then the second. "Light" cigarette vs regular ones don't have less nicotine necessarily (or less anything else - all the bad stuff is the same) it is advertising to refer to the lighter taste (while hoping you will think you are getting less or dropping down a level). So when you smoke lights you do not inhale any less nicotine they have just treated the tobacco to be less harsh and the flavor to be 'lighter'. So a two pack a day smoker of light cigarettes will usually be taking in the same amount of nicotine as a regular flavor brand IF the inhale the same number of puffs the same way.
Just as a rule of thumb for starters with e-liquid the idea that if someone smokes a pack or more a day was at least exposed to more nicotine then a person that smoked half a pack (and someone that smoked two was exposed to more then a pack a day user) so people equate that with the standard nicotine mgs of 18-24, and sometimes 36 mgs for a two pack a day smoker. While that is a starting point whether you need 18 or 24 or can even tolerate a high mgs of nicotine depends on how you smoked. A pack a day, smoking when you talked on the phone, worked on a computer or doing anything else might mean that a lot of each cigarette goes to ash in an ash tray and you are getting way less nicotine then someone who smokes while standing there puffing with each breath and no part of the cigarette burns up without being inhaled.
You could be on the right wavelength thinking you should try/use a lower nicotine mgs. It possible that even 12 mgs may be a stronger you want in a flavor and you might then even consider 6mg. You also want to consider that when you do use a higher strength then you are used to from smoking you can adjust what you end up with in an over time blood level of nicotine by hitting the PV more often or less often. Someone who chain vapes but was a pack a day smoker and goes with 24mg e-juice could find themselves getting ill over too much nicotine while someone who only hits the PV a couple of times and hour but was a pack a day smoker won't get ill at that level - because of the level they get in their blood. If your throat is getting too dry or sore but you want 18mgs or 24 mgs of nicotine for the throat hit feeling you should cut down on how many times you hit the PV in an hour. On the flip side if you hate the feeling of a throat hit and therefore want to use 12-18 mgs instead of 24 then do worry you won't get 'enough nicotine' - you can just adjust how may times you inhale from your PV.
My suggestion, beside what was already suggested that you try a 50/50 PG/VG or 100% VG and then consider how much of each cigarette you smoked when you smoked analogs as well as how many; you need to consider whether you sore throat may also be coming from the throat hit you are getting from 18mg of nicotine. Besides the PG/VG content you might need a much lower strength of nicotine - anywhere from 0mg to whatever amount you find has to harsh of a TH. As a side note I now of one person who went from smoking to vaping to find that although they burned up nearly two packs of cigarettes a day, anything over 6mgs made them feel sick. They liked the act of smoking much more then inhaling a lot of nicotine - a good portion of the time now they use 0mg e-liquid and only use e-liquid with nicotine content a few times a day instead of every time. That's probably not usually going to be the case, and from my own experience and what I have heard what others say at 12mg you should not really get a TH that is noticeable.
So there a a lot of things you can try until you come up with a good combination for you. Everyone goes through that when getting started vaping. For some the first e-liquid and the amount of nicotine they start with, the first battery they buy, the first carto/clearo they use are all perfect for them while for the next guy their start up supplies comes close to driving them to throw the e-cig ut and go back to analog, and then there are so many levels of in between you can't even list them all. Vaping is a personal choice and that personal choice extends to what you use to vape and what you vape. Sometimes it takes a while of trying different things - experimenting so to speak until you find what is best for you
