Looking for some experienced suggestions

This will be my first time growing and I want to do it right the first time. I'm hoping to be able to grow some amzing bud. I'll be ordering some crazy stains (G13 Haze, Alaskan Ice, and Northern Lights are at the top of my list) online and I want them to reach their full potention. Peopl have told me that as a first timer I might get some decent nug but it won't be what I'm hoping for. Here is my plan for growing.

Grow Box:
I want to grow 4 plants in my 3'x4' floor area closet. I'm am going to build a
6'H 4'W 2.5'D grow box. I will make it air tight with vents and reflective on all inside walls wilth 2mm mylar film. I was thinking it would be possible to avoid getting a reflector if I already have all sides and the ceiling covered with mylar.

Light:

I haven't officially decided about this yet. At first I was considering both a 400w MH and HPS for the vegetative and buding stages. I'm concerned that this might be unnecesary to get both. I was also thinking of just buying 1

Your cabinet size is pretty much the same as mine and I run a 400w cooltube. If you get yourself one of the newer "smart" lights that can run both MH and HPS bulbs you can MH for veg and HPS for flower and a single 400w light should be plenty. Careful with the Mylar when installing, from what I have read sometimes hard to put up without tearing or getting wrinkles and creating hotspots. As an alternative Koolseal white metal roofing paint has like 90% reflectivity, no hotspots and doesnt tear :thumbsup: and runs about $20 a gallon. I did all walls inside of mine with 5 coats and still have 3/4 of a gallon left.

are you aware you posted this twice?

Here is the run down: You can create a great first batch, my very first batch ever was NL with 3 plants in a 3 x 3 area with a 600W HPS. On that run I yielded 8 oz. cured. Of course that is puny compared to today, but still I think you'll do great.

Too get a good yield out of few number of plants you need to veg for a long time, like month or two! If you bring those NLs into bloom at about 16" they will finish at about 3'. So figure out how much exact height you have to work with and do the math as to how high you should veg.

you will be happier with a 600W.

You WILL be happier with a 600w.
Vegging plants for a long time in hydro is very difficult for a noob, especially running non-commercial strains that can't take much abuse. If you intend to get decent yield off ~4 plants, and just HAVE to run hydro, you will need to run large DWC units similar to waterfarms, like the ones weedhound built.
IMVHO.. start in soil and make yourself a mother plant to take clones off. Then switch to hydro when you can populate something like an ebb n flow with rooted clones for flowering.
Just fyi... hydro weed isn't in and of itself better quality. So make your style decision after informing yourself of all the options!