That's a good description of what you need to do, pretty simple stuff.
I don't know about the logging, you said " it shows the status of each connected circuit" so all you need to do is return the current status of each circuit. And most people are using JSON these days instead of XML. It's easy to parse in JavaScript, just eval() the returned text.
You can also use httprequest to send commands to the Arduino and avoid the hassle of reloading the page each time the user issues a command.