I dont agree ..
you will need some kind of ventilation to keep temps down ..
and to provide fresh air/co2 for your plants .. and so you can controle odour as it will stink ..
get sumthing like this:
http://www.ebay.co.uk/itm/250582211963?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
you wont regret it ..
I had 90ish degress in my 9x3 and 8 high room .. it dropd to 85F with the ventilation (82F with a big Fan at the HPS)
I dont have to worry about doors open or windows for fresh air (will also be a problem for you once they flower.. they WILL need total darkness .. and fresh air doing the dark hrs)
and my hole appartment dont stink from my 2 plants anymore .. dont have to worry about that ..
best investment I did .. better then my 600W HPS ..
now with that said .. relax .. one question at the time .. your clearly did`t get them basic in order ..
try to read a few guids to get a basic picture on how to grow indoor weed plants .. will also help you undestand the answer you get and help you ask the right questions ..
try one of this:
http://www.kindgreenbuds.com/cannabis-grow-bible/plant-problems-and-how-to-solve-them.html
http://www.420magazine.com/forums/how-grow-marijuana/81264-how-grow-marijuana-everything-you-need-know.html
boath are realy nice and easy guides .. use ½ a hrs please ..
about numbers of plants .. I would try 2 to start with .. will fit your 400w MH/HPS and you dont have to much to struggle with on your fist run ..
dont worry about strain .. as long as its weed
you will notice soon enough .. high spinkly plants with slim leaves are a sign of stavia or a stavia mix .. low bushy plants with tight nods and wide leaves is a sign of Indica ..
5 gallon pots will be a good size as end pot .. but I would sugges you to start in 1 gallon .. fist 2 weeks or so .. then give em fresh soil and more room in a 3 gallon for another 2 weeks .. then the 5 gallon .. give em a few days/a week to find ther feet/roots in the 5 gallon and then trow it in to 12/12 for flowering .. need fresh soil/more room for flowering .. plants will easily double in size fist 2-3 week of flowering ..
about nuts .. I dont feed fist two weeks .. after a few nods/leave points (4-5) I start slowly on nuts .. 1/4 strenges and move up slowly ..
try to find a nice start packet for soil/terra .. many hydro/grow stores online have a nice starter budget kit with small bottels with all you need for your fist runn .. I like the Plagron series .. have a nice packet deal at my store .. 35$ for a set with veg/bloom nuts .. and some nice stuff for the soil 5 small bottels in total ..
hope some of this help .. keep asking questions .. but please do some research yourself .. get the basic in order .. but in the end you will only learn by doing .. use the fist grow as a trail runn .. to learn and try out stuff ..