18 square feet would require about 1000w of HID light.. so you'll want a 1kw hps

to keep it simple, yet get the best/ fastest results id suggest you grow in 5gal buckets w/ drainage holes in the bottom... as many as will fit in your space... MJ likes to stretch her feet, so the more room for roots you give her, the better

if you like, you can get some air pumps and bury airstones in the bottom of your buckets... we call it SoiDro... it will increase growth rates by getting more o2 to the roots, but will dry out the soil faster, requiring more watering and feeding than normal... overall a small sacrifice for faster growth it will also make overwatering close to impossible - near hydro growth rates with simplicity of soil growing

i dont think you will get 16 plants in that space.. maybe half that... but remember the # of plants does not dictate yield, overall care is more important for getting those high yielders