Backups are taken daily. We save the latest two days, so the freshest copy would be from this morning and you'd have yesterday, plus a copy from last week and a copy from last month in case it took a while to detect a less obvious problem.
We look for a specific word or phrase on the front page of your site.
Yes. By default it's limited to the lower of 1Mbps (0.125 MBps) or whatever your server will allow over a single connection.
Yes, you can boot any of your four clones and log in just as you do on your main server.
Books have been written each covering just some of the security measures which are used. Assuming that you're not wanting a 400 page answer to this question, all we can say is that a full answer probably would be about 400 pages. We can say that we've been in the security and server administration business for twelve years and have a well known and well deserved reputation for being very sensitive to security issues. See our many posts ranting about all of the ridiculous security holes on PHP for examples. Given that your main server actually operates web sites and probably runs both FTP and PHP, we *CAN* pretty well guarantee that our systems are far more secure than your main server is.
Additionally, even if you DID want a 400 page response, one basic rule of security is "need to know" - you don't go around giving out all of the details of your security measures because that's exactly the information the bad guys need in order to try to defeat the security. See the recent articles about the new presidential limos for example - they give precious little detail about exactly what security measures are in place because keeping that information close to the vest improves security.