Yes, once a day. If a person has knowledge of nutrition and has a very balanced diet, then he or she may not need to take a daily multivitamin because his foods contain enough. I recommend each person take a multivitamin because many people don't have a truly balanced diet. Some people also need extra vitamin d, calcium, folate, omega3, etc..., depending on individual issues. Generally, there are no side effects.
Professional brand. It depends upon age and health conditions. Most of the easily availble vitamins do not support it fully and hence it would be a good idea to get it tested while annual physical and take it appropriately instead of flushing it out.