PG gives more throat hit than VG so you dont necessarily have to add VG. Straight PG doesnt create a lot of vapor though. VG is thick(like syrup) while PG is thin(more like water). VG creates more vapor and is smoother but also dulls your juice flavors some. Many people like a mix of the 2, like 80%PG / 20%VG. High VG juices are thick and dont wick as well in tanks/cartos.
A tank can be used with 100%PG but like I said, wont create a ton of vapor. You can just add some VG but it is gona dull the flavor some. If you do buy straight VG make sure its USP grade.