1. Your container size should be twice the plants height in gallons. Ex, 2 foot plant = 4 gallon container, etc.
2. Don't let ANY light interrupt the dark period if you can help it, if some gets in, that's okay but nothing brighter than a "pale moon."
3. They're not that yellow. Um... don't go crazy with ferts, especially N b/c your plant should need N much more during veg than flowering. Chances are equal that it could be something else. Go water, wait a day, then transplant.
g'luck