She is beautiful, and no you can't tell the sex, until you turn the light's back to 12 12, then you will know in about two weeks if she is male or female. You might want to let her grow for about two months, before tuning the light's back, and you need about a 1 1/2 gal to 2 gal pot, so you will need to transplant one more time. I think you mean about 20 watts, on those 75's. You don't go by the brightness of the light, but the actually watt. When you get ready to go to flowering stage, you might want to us 40watts bulbs, I don't think the two 20's will be enought to make much bud. Just to give you a better Idea, I have a 72" L X 32" W X48" H space where I grow mine. I have 9- 40 watt bulbs and the tempeture stays under 90 at the top. With one exguast 4" fan, and one to bring fresh air in 4" fan. Make sure your bulbs are side ways, and not straight up and down. You get a lot more light from the side of the light, then you do the end. Good luck, and happy growing.