I don't think you NEED to do it more than once a week, but if you want to, be sure that there is at least one day between this workout and Chest/Back (and the first use of S&H) because it can otherwise not give enough recovery time for shoulders.
I also recommend maybe doing it once with heavier weights at 10-12 rep sets, and the second time with lighter weights and 12-15 rep sets, just to mix things up.
Actually, definition is a combo of muscle (which you will get by working hard and allowing enough recovery) and body fat loss (which won't happen by doing work for the smaller muscles, but will get a boost by working the larger muscles, so S&H won't do much for it necessarily).