depending on the amount of time in veg one plant can fill that space but are you going to do a short veg time? I would say six is your absolute max...remember you need room to walk water manage your plants and such.
you have thirty days left.......think about it do you plan on flushing in the end? if you do plan on it in the final one or two weeks then and youu flush now......how much time does your p[lant have to uptake nutrients in the final thirty days? not very much people are dumb.... dont listen to...