4x10 is 40sq, thats enough for about 40 plants, and they'll REALLY be jammed in there. Or about 10 really large plants.

Best way to do it IMO is to grow out a mom, and then do clones, takes alot less time from clone to flower than it does seed to flower. The other alternative is to plant about 10 feminized seeds, pick the pheno you want (fast veg growth, good looking plant) and take that for your mom, or clone them all, and flower some out to see which flower the fastest (early girl pheno) and then use that for your mom. I usually use the early girl pheno, unless I'm going for exact THC/CBD ratios or something else.