Bunion/Fracture. A lot of that depends on the location of the other fracture but if you will be off the foot for the fracture, it may be a good time to consider doing both together in order to safe time off of the feet in the future.
Depends. If it is the same foot, the upside is you can stay off of it and both should heal. The downside is there will be more swelling and discomfort. If it's the other foot, it will be very difficult to get around with 2 bad feet.
Bad if opposite foot. Not a good idea if the problems are on opposite sides, as you need a stable foot to support your body weight on.
Could be a problem. Depending on which bone you broke in your foot, the added bunionectomy procedure could complicate your healing. If you have to be immobilized afterward for the broken bone, you would not be able to do physical therapy to ensure good range of motion at the bunion joint after correction, which could lead to a very stiff toe and pain afterward.
Possibly. While treating a bunion at the same time as a fracture may be appealing due to having one down time, additional surgery adds increased trauma to a small area of the body that can affect wound healing and increases your post operative pain. It is important that the reason you want to fix the bunion is out of symptoms and not convenience.