Andrew,
I forgot to mention anything about the volunteering that you asked about. As far as I know, you can never volunteer too much. The more the better. However, as always, quality is better than quantity. If you volunteered at a hospital and also spent some time shadowing a doctor it would be even better. Sometimes the best way to start shadowing a doctor, it to simply ask! Find a doctor at the hospital at which you volunteer (may be in the Emergency Dept)and introduce yourself. Tell them about your plans to attend medical school and I'm sure someone will be willing to lend you a hand. If you plan to apply to an Osteopathic Medical School and there is D.O. on staff, all the better! If you show enough interest and enthusiasm you might even get the doctor to write you a letter of recommendation. Remember, some osteopathic medical schools want a letter from a D.O. Try not to choose a resident or an intern. Concentrate your time more on an attending physicians. Although, both interns, residents and attendings have the same two letters after their name, the interns and residents are still technically students. Since attendings are more experienced and sometimes are teachers as well, they carry much more weight in recommendation letters than interns and residents. While you're working with the physicians, don't forget the nurses and techs who may be working there. They can teach you a couple of things too! As strange as it may seem, these people often know a lot more about medicine and patient care than the physicians. Try to make this into a volunteering as well as a learning experience. After all, you're trying to find out whether or not you would like this profession as a career.