Maybe this is the stupidest question in the world but I've been asking around n no one can give me an answer. If I hook up a 350 watts head to a 1,000 watts cab...how many watts am I really pushing out? 300watts? 1,000 watts? or what?
You're pushing out as many watts as the head can deliver, not the cab. The cabs wattage rating usually tells you its peak of how much it can handle. So in your case you're probably pushing out 320 watts or so.
Assuming the impedance of the cab matches the minimum impedance of the head, you're pushing the max that the head can deliver. The cab can deliver 1000 watts, but it can't deliver what's not there.