Your e-liquid consumption also depends on your vaping hardware, both PV and atty-cart/carto/clearo/tank. When I was using eGo batts plus attys and/or cartos almost exclusively, I went through about 3 ml. per day. Now that I'm using VV/VW PVs plus Vivi Novas and Vivi Nova Minis, I find I'm vaping about 5 ml. per day.
Nothing really changed: just my hardware.
I used to be a three pack-per-day smoker, but from what I've read here on ECF, the amount you vape need not correlate to the amount you vape. Some go from being less than PAD smokers to chain vapers; a few go the other way, from heavy smokers to occasional vapers. The nice thing about nicotine is that your body tells you when you're under- or overdosing. If you're underdosing, you'll most likely have heavy cravings for analog cigarettes; if you're overvaping, you'll get plenty of symptoms that tell you to slow down (without endangering your health).
So you'll just have to keep track of your personal consumption as time goes on. Just find your "sweet spot" for maximum contentment.
I will say that those 3 ml. sampler bottles probably won't last you very wrong!