1. Yes, you can. Look for USP grade VG in your local drug store or the pharmacy section at your favorite retailer, they usually carry it in small bottles.
2. Depends what ratio you're looking for. If you "make" 60 ml out of one bottle that's 80/20 PG/VG, you'll be at a ratio of 40/60 PG/VG, but keep in mind that your flavor and your nicotine will be cut in half.
If you're looking to get to the 20/80 PG/VG ratio, you'll need to add 90 ml of VG and make a total of 120 ml for that ratio, but that will be seriously diluted in the flavor department, and your nic will be cut to a quarter of your original purchase.