You dont need really need any background to use OSCommerce or Magento etc.
I will recommend doing the following;
1. Dont bother custom-made sites as it can be time consuming and expensive. Simply purchase (or download from BHW) a Templatemonster OSC template.
2. Go to OSCommerce.com > contribution section, look at the add-ons that's available, and what you are interested in adding to your site.
3. Hire a coder, have it installed the template and contribution to your hosting. This process should take no more than a week (at the very very MAX).
If you need help with the OScommerce backend, then either ask your coder to walk you through or hire someone that will do so.