[dnanian]

OK. Well, the first thing you need to do, before you start partitioning the drive, is create a Sandbox on a drive with a lot of space. Just try creating it, so you can see how large it'll need to be in your case.

Once you've discovered that, you'll need to do the partitioning (or, you can use a Sandbox on an external drive rather than partitioning and losing the internal space). You can't make a Sandbox and backup in "one step" - it needs to be made from the original drive, and I'd suggest doing so when you're actually running from it.

Remember: you must still back up - a Sandbox is not a backup. And you must back up the original volume, because that's where your data really is.