My 2 cents worth, oscommerce all the way, i have used it on several stores now. Never had a problem, it will handle 1 product up to thousands, nice easy to use admin, easy to change designs. very secure from what i have done and seen. It should take you no more than 20 minutes to set up the basic store, then a couple of hours to get it so its working, As long as you want to take making the look and feel how you want it.