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Here's some great information I found a while back on the virtualweberbullet.com site reference brining and containers. If the aluminum pan is all you have there are some great recommendations on types of bags you could use and still use your pan.
A ten pound breast? Does it have the breast and rib bone still attached? That's a big breast, as far as how many it will feed, it depends on how much they eat but generally about a pound per person. I'm guessing you will have sides too? That's usually how I estimate my quantity.
I would use a very clean bucket for your brining. I'm not real sure that the pot will react to the brine but why take a chance. You can even use a big turkey size zip-loc baggies too.