[dnanian]

Hi, Migo.

Yes, you do have to repartition the drive with GUID or APM, depending on your Mac's CPU type. It's not mentioned in the User's Guide because Disk Utility used to force the issue... but after this SD! came out they changed it...

Your Sandbox's size depends on the size of the files you're not sharing. Try creating one on a partition that's too large to get an idea... and, yes, it would be your primary startup when you determine you need to run from the Sandbox.