how many... well as many as your business requirements, and your analysis of those needs
how many tables and what are they...
as to what they are, see above
as a minimum you are going to need a table for products, and after that who knows.
do you need / want to store customer details, then you'll need a table for that
do you need / want to store customer orders, then you'll need a table for that
do you need to differentiate your products into types, sub types and so on,, then you'll need a table for that
do you need / want to be able to make suggestions of products which may match based on the customers previous purchase and or search history, then you'll need tables for that
do you need / want your customers to be able to search your products by categories, types and so on, then you'll need table(s) for that
..and so on.
E-Commerce is a generic term, what is suitable for a large multinational will probably not be suitable for a one man band
so you need to investigate what you mean by E-Commerce, find out what faciltiies you need to offer and support and develop your design from there. you may find some sample schema by using google
I'd rather be riding on the Tiger 800 or the Norton