Mt general rule of thumb is that a 3-gallon pot will support a plant for 3 months. If I'm going to be
keeping her more than 3 months I go to a bigger pot. 3 months = 13 weeks and that covers most
everything I grow. A 4-5 week veg followed by 8-9 weeks flowering should be more than enough
time to finish most any variety. (A few oriental sativas may take 10+ weeks to flower).
Stay with the 3-gallon pots and you will save time. Once transplanted into their final pot each plant
will concentrate on growing roots to fill the pot. In a 5-gallon pot you will waste 10 days or so while your
plant grows a bigger root system than you really need. They won't grow much aboveground until the roots
are done stretching, so you have to wait.
Good luck, BigSteve.