What type is right for me?
The type needed depends on what you're primarily going to do with it. Bar blenders are ok for light food, but extremely good for crushing ice (Margarita, anyone?) or quickly mixing various beverages. Food mixers usually have more features, options and speeds so you can process foods of all sorts of consistencies and varying degrees of frozenness.
What size container do I need?
Size of the container is determined by how many drinks or food items you plan to blend at a time. For restaurants with the signature daiquiri, where many are ordered at a time, a 64oz blender container may be a more practical choice, whereas the restaurant that just needs to mix milkshakes or other drinks on occasion would be fine with a 32oz one.