1. You can create an Event on any drive you want. Events are merely a collection of media files. You can name these Events anything you want, and you can choose to put them on any drive you want (although they must be connected locally).
2. The difference between a Project and Event is pretty simple. An Event is a collection of media files. A Project is what you might think of as a Sequence. The difference between a Project in FCPX and previous versions of FCP is that in FCPX, a Project can only contain ONE sequence. But you can create a new Project or copy and paste an existing project to create a duplicate for tweaking (again, Projects can be put on any drive you want), and from that new Project, you can access ANY Event (meaning you can use media files from any Event in any Project). One correction to what you stated in your question: A Project does not "live within an Event." Instead, what happens is, when you create a new Project, FCPX asks you what Event you wish to associate with it. It remains something of a mystery to me, frankly, as to why FCPX asks this, since you can, in fact, use media from any Event in any Project. Still, FCPX does ask you to associate an Event with any new Project you create.
3. There is no way to set a Scratch Disk. The whole concept of Scratch Disks is no longer relevant in FCPX. You simply choose which hard drive you want each Event and each Project to be written to. When creating an Event, just click on the drive you want to use in the Event Browser, right click and choose "New Event." It'll put your new event on the drive you chose. And in the Project Browser, it works the same. Click on the drive where you want your project to live, then click the + button at the bottom to create a new Project, and FCPX will create the new Project on the drive you'd selected. It's actually much, much simpler than the old Scratch Disk concept.
