First Real Grow

hey, i'm using 3 27 W Fluro's that output each at 2700 Lumens for right now for my plants, currently i have about 3 different containers with sprouts going in soil, 1 is a normal pot with one plant that is about 1' and about 1 month and a half in but its getting yellow spots on it? ( no clues to whats happening, plus yellow on leafs at bottom) , i have a second container that i'm using for sprouts, currently it has 4 sprouts of i think is Big Bud around the edges and in the center is white widow which has recently sprouted, now my last container is just a standard taco bell large cup which i just planted one ak-48 into. i'm planning to eventually buy more pots as I will be switching to a 400 MH with a Sun Deluxe Bulb (cost me my savings), i'm wondering can i fit 6 plants nicely under this 400 MH with plenty of space for future growth? also do I need to enclosure the space around it since i'm only growing 6? and one last question is can this 400MH do the all-around work (Vegg/Flowering)? ( I can't buy an HPS for now)