The transition to open water swimming can be a difficult one. I started racing in sprints last year, where most of the swims were in the pool. I then did a couple sprints with open water, a 600 yd swim at Lake Arrowhead, then a 500 m swim in Mission Bay. As you stated, it is easier to start to the side or back of the pack. There is a mass hysteria towards the center and front. I completed my first Olympic tri this year at Lake Perris. It is quite a different experience, the first 300 m is packed and you have to be prepared for people swimming into you. As this is only my second year, I thought the transition from sprint open water tri's to olympic open water helped my comfort level. Hope this helps.