First Time Growing, Suggestions On The Best Grow Box Setup!

Hey guys, my plan is to build a grow box that will fit inside my closet. Right now I have a 400 watt HPS setup that I was planning on using through the whole grow (veg/flower), but someone just gave me a 90 watt LED light. I really couldn't find any good info on LED's so my question is, should I use one for veg and one for flower, or both together throughout the grow? I don't know exactly how big the box is going to be, but I do want it to be at least 5 feet tall. I plan on growing 3 plants at a time, what would be an ideal size box? Thanks for the help!