You're lights should be as close as possible without burning your plants. Test it with your arm, if your arm can't handle it, neither can your plants. As far as how many plants per light...well, you don't want to use less than 2500 lumens for one plant.
How many plants you have should be determined by the size of your grow space, not your lights. Then you can determine how many lights you need...so how big is your grow space?
A for yield, that's not really possible for us to answer. Especially not with the info you've given us. If you told us EVERYTHING, meaning your grow method, your watering schedule, your nutes, your temp, your ph, your EVERYTHING, we MIGHT be able to give you and IDEA, but generally, there are too many variables involved for us to give you a real answer.