I would use more reliable services like MtGox, CampBX, Coinbase, or a trusted seller on localbitcoins.

Yes you can, this is a great idea actually, so that only one card (the one used for mining) will get much wear and tear on it. If you ran it full-time for very long, the Bitcoin mining card would tend to encounter errors and graphics glitches when playing games.

No, Paypal is easily reversible, and Paypal sucks.

How do we know you're sending the coins or fiat money to these charities and not just taking it for yourself?

A better solution is just to remove the restriction and let anyone post.

You can't create an account using TOR, so I don't see why there would be much abuse.

My two bitcents.