A good rule of thumb on your footings is at least twice as wide/square as the column. Depth and shape have a lot to do with soil conditions. Hard pan/clay you can go around 8 inches or more deep, with a flat bottom. If you have loose sandy type soil, then you should go a little deeper with a rounded bottom. Everthing that 700LH has said, too! The only other thing I can think of is make sure that your brick mortar has fully set before you fill the column with concrete, and when the time comes, slop it in as gently as you can. I have seen many a brick column come undone from pouring the concrete in too soon, and too fast. Good luck with your project.
R.
