Generally speaking, if you use 100mg PG nic and aren't allergic to PG, you can do pretty much whatever you want with the juice while maintaining your ratios and working with PG is easier than VG as it's not nearly as thick.
If you are attempting to make juices near to max VG, then definitely order your nic in VG. VG also offers the most versatility as virtually no one vapes 100% PG juice, so you can always add VG nic to reach desired ratios. This only applies if you are using 100mg.
If you are using anything less than 100mg nic, order it in whatever the predominant % of your base is.