Whats up Mmayhemm ,
As a general rule ppl. try to shoot for 50 watts per. sq. foot .
5 ft. X 5 ft. = 25 sq. ft. X 50 watts. = 1250 watts . I'd go for the 1000w. hps or a switchable ballast . I have good luck w/ a EYE hps hortilux bulb start to finish .

What type of hood / reflector do you plan on using and how are you gonna cool it ?
1000w in 150 cubic foot of space will rock if you can keep temps down , but I sure don't see 4-5 plants in it . They get crazy huge fast , you'll see .
Peace
Crispi :thumbsup: