There are a lot of manufacturers who will custom mix your e-liquids as to Pg/Vg ratio and nic concentration. One that I've used is Virgin Vapors, but there are many more.
I frequently add Glycerin USP to my e-liquids. Produces more vapor, smooths out some harsh flavors (with too much Pg), extends the use of a particular flavor.
Never add more than 10% distilled water to your e-liquid. Our vaporizers do not vaporize water well.