Re: removing moldy drywall
I would treat it as surface mold first, unless you know moisture has penetrated the wall. Use a bleach solution to clean the wall surface, then repaint.
If you know there is moisture damage/mold inside the wall, then remove the drywall as necessary to access it. Again, use a bleach solution to eradicate the mold. A dust mask wouldn't be a bad idea, though finding one that can filter out mold will be a trick, for that you'll need a vapor mask. You can still treat the wall with bleach, which will cut your exposure to the mold, before you remove the damaged area.
When removing drywall, you can do it the easy way and simply cut down the side of the stud, or, you can take the time to find the center line of the stud and cut it there, the latter method will make installing the new drywall much easier. You can start with a smaller area than needed, just to make sure you need to remove anything at all. Cut this area clean and even, if there is no mold, you can use the piece to patch the wall back.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!