3x3x6 400 watt tent grow SOG

Hello everyone, So I've decided to start a little operation, and I thought I'd share my progress with everyone as well as hopefully get some tips along the way. This will be my sixth grow, three have been outdoor and two indoor, and all my past grows have been small scale. I'm gonna try to keep this OP short, but I would love any recommendations along the way. I ordered a "complete grow tent kit" from www.htgsupply.com a few days ago. It comes with a 39"x39"X79" tent, 400 watt hps, and tons of other stuff like fan, filter, grow bags, soil, nutrients, and thermometer, etc... I also upgraded the nutrients to the Fox Farm Trio (wishing I had Advanced Nutrients), and the soil to Fox Farm Ocean Forest. I additionally purchased Fox Farm Sledgehammer, kelp extract, and some other stuff (I forgot exactly). I also bought a brick of coir just in case I didn't have enough of the soil. I also have another 125 watt hps that i'm debating on whether to use for my mothers or for additional lighting during flowering. I soaked about 25 seeds (bag seed I have collected over time from very good bud) last night and are sitting in paper towels right now. My plan is to sprout around 20, and then pick 12-15 of the healthiest looking ones to veg, hoping to get around 6-7 become female. Also, I will be taking clones while vegging. I'm gonna try to keep it down to 6 or 7 flowering plants for the first go around, but I was wondering for future references how many plants would be ideal for these dimensions to get the best yields through SOG. Originally I was also gonna blend some of the coir with the Fire Fox Ocean Forest along with some perlite. Is this recommended? And also, can amendments be added to FFOF (as I was told it was pretty hot itself)? I'm just in the germination and setting up process but I'm very excited about this grow. I will start putting up pictures soon and hope that I can get tons of input from everyone. Thanks, KBUD