What size wall can a gallon clean?

Spraying seems to be the most popular way to apply this product. However, I paint it on the molded surfaces with a paint brush to be sure I get good coverage. This seems to save the product somewhat. So, if you paint it on, it should cover about as much as a gallon of paint with a single coat, 40 feet X 8 feet or about 320 square feet.

what type of breathing mask would I need to block the product from being breathed in while cleaning?

I used a fogger and stayed out of the area. It is low odor. Organic vapor mask would be really good. This from the web site: Do I need to wear a mask when using Concrobium Mold Control?Concrobium Mold Control does not contain any VOCs and does not off-gas. However, if you're in an area with heavy mold growth, a mask would be a good idea to limit your inhalation of harmful mold spores. If fogging, it's a good idea to avoid breathing in excessive moisture from the fog.

Can I clean my dishwasher with this?

Honestly, my parents use Tang (the powedered orange juice mix) to clean the dishwasher. They run it without dishes and place the Tang where the soap goes. After the dishwasher runs it’s course with Tang, it’s sparkly clean!