My biggest piece of advice is at least buy a bunch of nic now and stick it in your freezer. Even if you don't start mixing right away, you know you have a stash if nic concentrate suddenly becomes difficult to obtain in the US (yes, if those wonderful FDA folks decide to come down on
vaping hard, that's the biggest blow they can throw). I get mine from Heartland ~$45 liter+shipping. There are lots of other vendors wit similar pricing ~$50. Check the DIY forum for others.
Just do the math on that. 1 liter of 100 mg nic can make 10 liters of 10 mg juice. Calculate to your own use (I'm at 6 mg so ~17L). That's a lot of juice for $45 worth of nic. Even with the cost of PG, VG, and flavorings, you're still down to pennies a bottle. Compare that against your retail juice prices. Obviously it only works in your favor if you can make something you like, so recipes are important.
I have ~3L in my freezer right now (probably get a little more as just because) I break down into smaller bottles so I don't have to pull a liter out to get a little bit to use. I have a 30 ml bottle in my mix bucket I fill with nic that is stored with my flavorings and I use that for my actual mixing. That way very little is ever exposed to higher temperatures. The reason is nic will break down a bit over time at room temperature, maybe a year (?). OTOH, nic in your freezer should last many years. Consider it a buffer against risk for your old age.