if you are growing a bunch of tiny plants you could veg for about 2 weeks(or whenever a good root system is established). if your thinking of doing a big plant i would veg for at least 6 weeks
umm.. well.. there is a lot that goes into how much you yield.. what size light are you going to use when flowering?
if i veg for 4to 6 weeks and flower for 8 weeks....how much bud could i expect of each plant when dry......i got 10 plants??????
.....you should yield about 3 lbs.. your asking quite a bit of questions. there are a lot of tutorials and guides you could read.. your not a cop are you?
yield is heavily dependent on strain,lighting,enviroment,nutes,how big container is,etc... check out the grow journals and find a strain you like and can do, and most of all....read the stickies and use the search feature...there is GOBBS of info on this site. good luck