Pot size, sexing advice, soil mixture, lighting...

Hi people

I am a new member to your site but a second time grower. For my first grow (closet set up, beautiful end product) I came here for lots of advice, however this time I have a specific question...or two. I also thought it'd be nice to join the community and share my happy experiences over time, maybe even pass on some wisdom one day.

Anyway, my questions:
I am growing from seed again as my first batch was from cheep seeds and I want the mother plant to eventually be from something that really kicks ass! So, I want to grow at least 10 full size female plants. So I figure im gonna propagate 20 seeds?
Im a fan of getting the seedlings into their eventual pots as soon as possible so what size pot should I use if I am hoping for about 3oz of bud per plant?
Also, I want to try sexing the plant by flowering one branch with a bin liner, does anyone have strong views on this?
Finally, Im building a 6'x6'x6' grow box for the flowering cycle. Im thinking either one 1kw HPS or two 400w HPS with some fluorescent strip lighting down the sides. What advice do you have on that?

Oh one last thing..... I am using soil to grow them and used a 50/50 mix of compost and worm casts last time, but im thinking of making it a 1/3 compost, 1/3 worm casts, 1/3 SHARP SAND to help drainage?? and maybe adding some fish, blood and bone mixture to it for some slow release fert??

Thanks so much for your invaluable advice. The time you take to help us newbies and relative newbies is greatly appreciated.

Smoking makes me happy...its that simple.

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U should change the dimensions 6x6x6 sounds a lil shady haha good set up tho
Wut did you mean by flouro strips? Just mini flouro's??

4'x4'x6' is all you need for ten plants. Im not sure, but i dont think you want to use sand in your mix. I would substitute it with perlite.

natural sand in the mix is fine, just not manufactured sand (alot of chemicals) And it should be like beach sand and totally non cohesive without any silt. It's like perlite and helps drainage. Not too much though. Some people use sand on top of their soil to discourage gnats, others like to use hydroton for the top 2 inches of the pot for erosion protection, to keep from washing the soil away from the roots closest to the top of the soil. It's kinda up to the grower