Swulll, just do the arithmetic.
If your substance is 250mg/ml and you want to run 500mg/week, that's 2ml/week. A cycle of 12 weeks therefore requires 24ml's, total. Most sources offer 10ml vials (some offer 20 ml vials), so 2 vials won't be enough, and 3 vials will give you more than you need.
Def go with the 3 vial order. If you read a little more you may get to thinking a cycle of just 10 weeks would make all the arithmetic work out nice and neat for a 2 vial order, but don't give in to that temptation.
Even experienced users will tell you they don't get 10 draws of 1 ml each from a 10 ml vial, 9 is more likely, 8 is not unheard of. Not talking here about you getting cheated by a source who underfills his vials, either. Remember that part of proper injection technique is to get any air out of the syringe before you inject, you will push a little of your aas out when you do this, and some people do it willingly to lube the pin a bit so it glides thru the muscle. And,when the vial gets down to those last few ml's it isn't as easy to draw as when it was near-full. As a beginner, your technique may be a little sloppy and waste a little greater, so buying a total of 30 ml's of substance for a planned 24 ml cycle is not being too extravagant.
You cannot overdo pre-cycle study of proper injection/sterility techniques, take your time. You may have to over-buy your pins too. "Wasting" one of them to practice injecting water into an orange is not as silly as it sounds, just trash that pin before you begin sticking you.
