I have 7 square feet, approx. 5' by 17" I have a 250 w mh light, do I need a larger wattage, a 400w or am I ok with the 250 w.
250W for 7sf is 35W/sf which is pretty bright. What are you growing? 35W/sf is more than enough for seedlings and low or medium light plants, you might even burn some plants. With a good reflector system you could be getting in excess of 2,000 foot-candles which would be enough for almost any plant.
I am starting tomato and pepper i was figuring about two feet above
Sounds about right. I don't grow tomatoes so I can't promise anything, but the numbers are right.
Most reflectors illuminate square areas. Unless you get a light mover, the ends of the 5' bench will be too dark. A 3' x 3' area would work better.
I will be using some reflectors to move light to ends.
That will help, but you are still likely to find the plants toward the center grow faster and stronger unless you move the lamp or the plants. Since the plants won't be under the light for all that long, the cheapest solution is to move the flats around every couple of weeks.