at 1-2mg, you'd be fine with 48mg base...
For perspective, that's about 20 drops per 30ml of liquid. So if you get something like 500ml of 48mg, that's enough to make
12,000ml or 400 bottles of 30ml. ( at 2mg)
I recommend 48mg for the simple reason that it's easier to mix without risk of hot spots (section of liquid that didn't mix correctly).
That could last you a very long time.
Remember that you should divide your quantity and put your "stock" in the freezer for long term keeping. the base (VG/PG) does NOT freeze, but you should let it come to room temperature when you're using it otherwise, it's very thick. I always keep a small bottle around with my flavouring and refill it once empty or low.