need help fast

i have a no. questions first some of my leaves are starting to get brown spots
any ideas
question no 2 when do i transplant as i sais the plants might need a bigger pot?
question no. 3 plants only 1 ft in height after 3 weeks but the plant grows to 3 ft and is meant to be ready to harvest in 8 weeks when should i switch the lights to 12/12 cycle ,using 500wt mercury vapour lamp


please help me please with these questions :confused:

I am not really sure about your first two questions, but on your third you should at least wait until you see signs of pre-flowering. You will start to see signs of the sex appearing and calyx development starting to form. After this is is pretty much up to you. You can let it grow longer to get bigger or you can flower it soon after, just depends on what you want to do.