You got it Ludvig08
The AG would save you a step, make it much easier for you when first starting out mixing.
I really don't worry about thinning VG unless I'm going with more than a 60/40 ratio of PG/VG.
One thing you may want to think of is how you vape, if you use cartridges, cartomizers, or tanks you may want to make sure you're thinning your VG down a little so your liquids are thinner and wick easier, if you're mainly dripping you can get away with running thicker juices.
Also, if you do plan on thinning out VG on your own, I would advise not to use ordinary tap water, make sure you use deionized or distilled water.
I hope this helps, it's all up to you, which is what I love about mixing.