The key to the Internet is integration. Front office systems must be interfaced with the back office systems. Gone are the days when you could have an HTML form drop into a mail box for manual keying into an order system. This may mean an alliance with your suppliers, or cause a relationship to be forged with other companies that you never would in the traditional business. Take the time to look at the value chain.
Payment is another issue.
With the issue of speed and convenience you can not afford to batch payment processing. You must integrate this as well. When an order comes in the payment authorization needs to be part of it. Simply put, when a customer comes to your web site and places an order, when they get the confirmation back, it must be for an approved, stock verified order. Conducting business is not as simple as it was several years ago.