I think it's like chief and others have told me before; it's sometimes hard to pin point how much is a "normal" amount to vape, because there are lots of variables: different brands of vaper pens, wattage, pg/vg ratios, nicotine levels, etc...
I don't know if this helps "limit" me- much like plate/bowl sizes limit food intake/portions; but I have 2 $20 pens (vapepin plus) they both have 2.5 ml tanks; however, I only fill to 1ml-1.5ml (approx half) I fill one tank with a fruity flavor- and that one is always ONLY for fruity flavors. I do the other half full of dessert, tobacco, root beer, ect and that tank is only for those flavors. Some days I never refill either of those two tanks, which means I'm only vaping 3ml a day. But sometimes I refill one or both of those tanks with another flavor; but again, only half full, so that would mean I vapes 6ml a day. I have never had to refill more than once a day unless I filled less than half on a vape I don't really like as an ADV, but still like a little taste now and then.
I'm finding its a lot like food and drink; you can sip on juice or root beer or munch on fruit or gum all day, but when you sit down to eat tiramisu, or cake, a little goes a long way. At least that's the case for me. But in that case it gets a little trickier to keep track of, cuz I will put in less than 1ml of tirimisu, then later fill it halfway with ry4life or chocolate Bob ( chocolate root beer float) for the rest of the day. Or a tiny bit of one fruit flavor like peach, so I can switch over later for pear or pins colada.
But generally speaking, I would say I vape between 3-6ml a day, but am surprised cuz it seems like I vape pretty much every few minutes every waking hour, so I would think it would actually be a lot more....
Like I said, a little confusing, but you'll figure out your sweet spot, then it will be more of a routine and you can plan your orders better and budget easily. A lot better than analog cigarettes; where you may smoke a pack one day and almost two packs another day. Usually, vaping is a little more specific in the amount you're using, so you can say, " oh crap! Im down to 5 bottles (or whatever) I go thru one every other day, better get online and re order or head to the smoke shop!"
It will get less confusing and overwhelming as you go, and soon you will be trying new things because you are curious, not just because you are running around like a chicken with your head cut off trying to get everything "just right." Good to start out with less, keep up with this forum, as well as others, try a new thing here and there, google questions, etc... You'll learn a lot. I know I sure have! It's almost more of a hobby than a habit! FUN!