A blackstar 500 should only really use about 270-280w (about double their '240w'), but you still end up getting a good $ per watt charge.Not sure how large your full size fridge is, but unless its the large casket style fridge I can't imagine you having much room for more than 4 plants unless you were going 12/12 from seed
Not sure about who makes the best organic nutes, but I've been using the Earth Juice line without trouble