Thanks Basara,
Your help is appreciated. On point 2, maybe the easiest way for me to describe what I mean is for the database to hold an sku number & a serial number. After reading the links provided, it looks like AbanteCart is possibly too restrictive for my use, I've outlined the reasons below.
1. Looks like you can only add products & discount vouchers after checkout, rather than adding a fee, such as a shipping cost.
2. Can only hold one unique id number.
3. I didn't look at import/export functionality due to the other limiting factors.
4. No access to css file to adjust the look, feel & design of the web pages. Only block editing available.
If I've not fully understood AbanteCarts functionality or use, any pointers to help me understand it better are appreciated.
Thanks again.