lvgxtuan
Ok you are going in the right direction... 400 hps will work well in that size of room. Above plant distance will be approximately on foot depending on air circulation. One way to check is to have the light on and put the back of your hand under the light.. move your hand closer until it feels hot after a minute or so. That is about how close your plants can be.
You will need some odor control, a carbon filter will do the job. Keep reading, reading, and reading. There is a wealth of info on this site but you have to read a bunch.
good luck
mustang