I setup daily, weekly and monthly backup for both the web and its database by using tar and mysqldump, then download them manually to the home system. Now the home system is not a 'live mirror'. I will set auto ftp to download backup files from the web host and restore them to the home system automatically. However it will depend on if the web host allows its customers using auto ftp. To make the home system a live mirror, there are still lots of works to do.
'that will be a lot of traffic on your home line' is one issue. Another potential problem is that the web host probably won't allow me to do it.