Online store / e-commerce

I've developed a fully functioning PHP site that pulls it's information and inventory listings from a MySQL database. However, the owner now wants his inventory to be bought directly online for increased sales. We discussed ebay and paypal and decided maybe we should directly integrate our own store into the preexisting site, complete with a shopping cart.

I know that these sites must transmit data using ciphertext and not cleartext and must have certificates and secure socket connections - I've never done any of these things before. Is there a good place for me to start, I'm a quick learner.

Any Advice, tips, Hints, ????

Ok... Did research, and came up with:

Step 1.)
Decide on using a Pay Page, or API Integrated Merchant account to handle credit cards. Pay page limits personal liability in terms of credit card number loss and theft, as well as removes the need for you to obtain SSL connections and certificates.

Step 2.)
Complete the PCI DSS (SAQ A) questionnaire to confirm compliance with online store regulations.

Step 3.)
Setup a user registration system and a table for users and a linking entity for their purchases in the database, and add prices of items into the database for each item record that the Pay page can reference for price.

Step 4.)
Handle things like accounting, shipping, currency conversion (if international sales will be occurin), and other basic and advanced functionality.

From what I've learned, these are the four major steps of starting an eCommerce site. Any other help?