No, a 600W will not raise any suspicions as far as energy usage goes. However the heat could be an issue. IMO, an air coolable hood or a cool tube is a must. One thing you could do is to get a dimmable ballast. A lot of them are that way now. They generally have adjustments like 250W, 400W, 600W, and sometime super lumens. Each different size of ballast has different dim settings.
I wouldn't use some seeds you just have lying around. There are several reasons for that. First and number one is the chance that if they are bagseed, they are also from hermie stock. Second, you really do not have any idea of 1/2 of the genetics. It could be something good or it could be ditch weed. Third, there is a real advantage to knowing what to expect from a strain--is it a heavy feeder, does it get tall or grow short, what kind of high do you get, etc, etc. It is going to take you about 4 months to go from seed to finished product. Are you willing to spend 4 months on an unknown product?
A 32" x 32" tent is so small that it would be quite difficult to partition part of it off. If you cannot get more/better lighting, just go with what you have. A 250W is not ideal, but it will gow some bud and how good it turns out is up to you. The dankness is generally determined by strain and the growers ability to give the plant what it wants. The lack of lumens should not affect potency that much, it will mostly affect yield and the buds will probably be a bit airier. However, there is no reason that you cannot get some frosty buds.