The only Theatre system worth getting.As for a real answer.
600 watt power for simply the speakers? Or for the whole system, for just the sound would be overachieving things, unless your looking for really loud parts.
1) Do I really need expensive cables?
No, well, it could depend on what system your using, if your going to have 500 volts running through your cables. (So that you will be able to shoot rockets out of your television!) Then you might need larger cables, but regular copper wire should do the job for just about anything.
2) What should I look for
I wouldn't go for sony. Have yet to find an impressive
cheap system for tv's. But samsung is good enough for me.
3) What's a good Watt range for powering an average sized open area ?
Again, are you talking about the whole system or simply a sound system? And by average size, you mean about 20x30 feet?
4) Are stand alone recievers better? Or dvd+recievers just as good?
I've always used standalone. It helps me figure things out when theres a problem.
5) Do sound systems draw a lot of power?
Depending on how loud you want them. Not sure how many Joules on average.
6) Anything else that I should know
Put a question mark at the end of a question...
and Ummm...
I would recommend that if you care about the sound of your movies so much to get a 3-way speaker or higher. (5-way is highest I think) They produce a better range of sounds.
I would recommend a projection television.