When i was doing soil grows i always planted right into the pot it would grow in.You remove any chance of something going wrong when you transplant 2 or 3 times like most people.
With a small grow space,with that bulb,you can fill it with plants and be fine.You will need to be able to bring in fresh air for cooling to keep the temps down.I would not say using that light will be a waste for one plant.When it gets bigger you will reap the benefits from it when it buds.
When you set your light up over your plants,start them 10-12 inches above them.put your hand at the top of your plants and see if the heat on your hand is bearable.If you cannot keep your hand there without discomfort,move the lights up some more.OPH