How long should I veg??

This is pineapple Kush almost 4 weeks old. They are about 10" tall. I am using A/N sensi grow in a DWC system. My room height is 7' tall. I would like to get the biggest yeild possible. They are really bushy as you can see from the pics so I dont know how tall they can get. I would like to know how long you guys think I should veg these girls (at least I hope they are girls). That brings another question when can I tell what sex these plants are? I know I can start the flowering stage whenever I want but I want these babys to Thrive so please give me your opinions. Thanks in advance for your opinions and help.Attachment 294145Attachment 294146Attachment 294147Attachment 294148Attachment 294149Attachment 294150

how many plants, how large are your flowering buckets, how big of an area, how much light do you have?

3 plants, one 18 gallon tote "DWC", Room is 8'x6' with 7' ceiling' One 600w MH