Those yields in the seed descriptions are for a best case scenario. Think of it kinda like automobile sellers. They told me my Scion xb would get 34 miles per gallon. Well this is with the windows rolled up, a 90 lb. driver, no passengers or cargo, all systems working perfectly, tire pressure to maximum, and a mild tail wind. In reality I probably could get 34 mpg, but I would have to do a lot of tinkering and maintenance, and find the perfect conditions. I also would have to be an expert. Since that stuff aint going to happen, I get 28 miles per gallon.

Same deal with seed sellers. You have to be an expert, and have all the conditions perfect to get the suggested yield.

And it's been my experience that usually a little more than half turn out to be female. More like 3/4. Don't expect 100% survival either, but you just might be able to make that happen.

And please allow me to be blunt. You are thinking a bit too much about the wrong things for a first grow. If you end up with any weed, you did good and reached the goal. Don't care about the yield so much. Just aim for a first time success. Think about things like the physical grow area, PH, nutrients, ventilation, lighting, odor control, and stealth issues. "How to" stuff, not "what will I get" stuff. But hey, that's just me.