You said you have (what was it 9x4 feet)
I think the basic rule is a g per watt. so if you have a 600w system them you could get 600g, 1000w = 1000g.
The longer you allow them to vegg the bigger they will be in the final stage. How much hight space do you have ie 8'.?
If you are going to lp then you will get around 1/2 oz per plant (+-) with 600w system, the trick will be to grow many many(30+) plants that are only around 8"-12" tall when they go into flowering. You will remove all lower leaves and branches so you only have the main top cola, this will also give you a very tight and dense product. Doing this will allow you to gave such a large amount of plants. You can use solo cups or 4x4/6x6" rockwool cubes.
Good luck and hope this helped