Actually pg enhances flavor and vg creates more of the vapor. Throat hit is usually from the nic itself. Some of the vendors nic has a more peppery taste to it hence the throat hit. Some of the vendors offer a smoother nic because a lot of vapers prefer it and like no taste at all in their nic. Neither is wrong its just a preference.
So lets use your 18mg/ml as an example. You could buy nic @ 18mg/ml from a number of vendors and some of them will even do a 50/50 pg/vg mix for you. But by doing that when you add flavoring to it, then the actual nic strength will go down a bit. If that works ok for you on starting out then its ok to use this. If you want to maintain the 18 mg/ml in your finished ejuice to vape, then you need some higher nic to accomplish that.
If you buy a higher nic base in pg or vg, then you will need to adjust the amount of your nic, pg, vg to get where you want to be.
Make sense? Let us know what recipe you would like to make and we can go from there.