will answer a few of your questions, a 600 would cover a 4 by 4 ft area that would give you the recomended 50 watts per sq ft you could use it in a slightly smaller area like a sq meter also and put you over 60 watts per sq ft.
first would recomend that you look at air cooled reflectors wether it is a cool tube design or a traditional reflector that can be air cooled it really doesnt matter, most of the heat will be produced from the bulb and you will have less temp issues if you go with a better reflector and a good 6 inch fan or equivilant blower.
for ideal growth you should use a metal halide or conversion bulb for veg and a hps for flower but many will use a hps from start to finish and there is not that big of a difference in growth when using a hps from start to finish and if your on a budget you would be much better off just using a hps and instead of buying a conversion bulb put it toward a better reflector and fan.