1. Are bags rated in C or F ?

In the US they're rated in F.

2. If a bag is rated for 0* does that mean it can be 0* in your tent or 0* outside?

In your tent.

3. If the bag is rated for 0* does that mean you WILL be comfortalbe (avg. person) at 0* air around your bag or does that mean you WILL survive but probably be pretty cold?

It's hugely subjective. They're trying to rate it so that the average person is comfortable, but everyone is different. It also depends on what you're wearing, what you have under your bag, what you ate for dinner, how tired you are, etc.

4. What type of fabric/material is good for a down bag to prevent water? My current bag is poly fill and I want to go down next as i've heard great things about their warmth as well as nwe style water-proof shells.

All the bags I'm aware of have nylon or polyester ripstop shells. You DO NOT want a waterproof shell. Water vapor from your body will condense on the inside of the shell and soak the insulation, making it worthless. Down bags are great - light, compressible, warm, all that. And totally useless when wet. I usually use a down bag in dry conditions and a synthetic bag in the snow.

5. Are bags temp. rated based on the occupant being fully dressed w/beani or undergarments only.. or ?

Dressed.

6. How can the same brand offer a 600Fill down bag at -20* and also offer an 800Fill down bag at -20*. What exactly would the difference be as I thought the more fill the more warmth so i'm guess less quality down?

Filling isn't the only variable. Bag construction, baffling, etc. make a big difference.

7. For my temp range of 30 down to 15 w/winds picking up every night to 10-30mph avg with gusts to 60 using a thermarest pad and sleeping in udnergarments what temp bag would you guys suggest?

I'm probably an average sleeper as far as temp ratings go. And your range is right on the border between a 3-season bag and a 4-season bag. If I thought it was going to be 30 degrees, I'd take my 20 degree rated down mummy. If I thought it was going to be 15 degrees and windy, I might even take a 0 degree bag. Since you say you sleep warm, you could probably get away with a 15 or 20 degree bag. You can always buy a thin bag liner to extend the temp rating a few degrees.

Kevin B.