I thought of something else you might want to consider, along the lines of what suzeeq said. If you practice doing your cast on in the same way until it becomes habit, you could run into a problem when you knit into it. The cast on needs to be loose enough to knit into and new knitters tend to cast on too tightly. Until you knit into the cast on you won't know if you got it right. IMHO you should knit a row after you cast on just to know how things work as you go along.
I should never overestimate my basic arithmetic skills.