It will probably take 1-1/2 boxes. Fill the pan roughly half full & use the rest for cupcakes.
Obviously, you need a need a new brownie tin! If the brownies ran over the top of the pan while baking, that pan is too small for the amount of batter in your mix or recipe. Use a larger pan.
The purpose of a brownie pan is to make a brownie perfect size and cut it (if you want to cut it). Then you can eat the delicious brownie.
The Perfect Brownie Pan phone number is 1-800-531-7935.
WHsmith
NO!
You run the risk of the brownies sticking to the pan or burning.
If you are using a 2" deep cake pan you would need 13.5 cups of batter.
Well... before you put the brownie batter into the pan... you have to grease the pan first! You have to put 1 full tbsp of oil ONTO THE PAN and then spread it everywhere in the pan. Even on the sides. You're welcome! 
The More Corners Brownie Pan has its own website. You can buy it from there or Amazon or several other websites. They do sell nationwide, so call baking stores in your area to see if they have it for sale.
It depends on how deep the cake pan is.
in a half sheet pan you need to batter at medium speed because if you batter it too fast the batter will be too rough ,or if you batter it to slow the batter will be come thick . so if you need to have the right speed with is medium speed and in the half sheet pan you will depend on how big your pan is and approx. 1/3 of a medium mixing bowl