The ecommerce system we use is good for tens of thousands of products or just one product. Products can have attributes, e.g. colours and sizes and also variations with different prices.
There are options for live Australia Post rates for different weights, standard or express post, or flat rates per item or per order.
Payment options can include Credit Card, PayPal, eWay, Bank Transfer or Cheque.
Product details can be entered manually, or imported from CSV spreadsheet files.
Products can be in categories, sub-categories, sub-sub-categories, etc. A product can be entered in more than one category.
See some ecommerce examples:
These are all built using WordPress with the WooCommerce plugin.