The plant's sex can be determined once it is grown enough to show it's reproductive organs. Keep a close eye anywhere after it is 12" or taller and you should be able to find them. 12/12 should work depending on the strain. Please inbox me for further questions and I would be glad to help!
These two ideas put together. Supplement the 400 watt with LED light as well, use outside air to cool the room. Blast'em with extra light. Dial in the other variables in anticipation of higher yield provided from the doubled lighting.
I've had wind burn before. When I did, I moved the direction of the fan from directly on the plant to pretty close to the plant so that it still moves around, but isn't constantly bombarded with the strong air current provided by our great friends at Hurricane.
Bloom nutrients often exclude nitrogen because as the plant gets closer to flower, it no longer needs as much nitrogen for vigorous growth. Yellowing is normal during these phases. That being said, a small bit of nitrogen can be helpful in greening up a yellow plant.
Not all growers add late...
From the Topsoil layer to the topmost shoot, it should be 20" to 30" before flipping. Stay closer to 20" if space is restricted, and always keep in mind that the plants will continue to grow taller even after you flip the lights.
A great example in my experience was watching the difference...
I have always been a fan of 9 per light 3 wide by 3 long. This breaks up infestations or infection into smaller groups that can be easily removed with minimal loss.