You forgot the most important item that I find with many of the clients that come to me for help fixing their websites, and that is making sure that people can actually buy something from the site. It's not unusual for the purchasing process to be so non-intuitive that people can't make it to the end. A recent client here opened their website several months ago and hadn't had a single sale from it. I gave them an assignment to use their site and buy a specific product from it. They were surprised to discover it was impossible to do so ... they'd never actually tried to see if the system worked or not.
I've fought a couple of clients over registration. They argument is always something like "Amazon uses it" without ever thinking about how it makes the process more difficult and the more difficult something is to use, the less people tend to use it. It's a personal peeve of mind to have to register just to give my money to someone to buy from them, and in fact often choose one vendor over another just for that reason. It's really easy to buy somewhere else on the web, so make it easy or let your visitors spend their cash elsewhere.