Yes, you can put all of that on one drive, long as it's not the system drive, correct.
Larry Jordan started teaching a media management system for legacy FCP using two drives, as he told me, to avoid his perceived possible confusion of newbies. Put files FCP ingests itself on one drive, all project, photo, audio, graphic, etc, files on another. The only reason was to avoid confusion.
I've found over and over it didn't avoid the confusion and lots of folks have twisted it into all sorts of wacky ideas.
So, you have ONE "media drive" that is NOT your system drive.
It should be either internal or FW800, either way should be 7200rpm.
Your media will be stored in two places:
1- Media FCP ingests via Log & Capture or Log & Transfer. That always lives in your Capture Scratch folder. Create a folder on your Media Drives called "Final Cut Pro Documents", point FCP's scratch disk settings (all of them) to that folder. That's a big folder and will be huge to back up due to the massive size of video files.
2- All other files related to a post-production project will go into what we all a "Project" folder. On the Media Drive, make a folder called "Projects". Inside that you will make a sub-folder for each project you have to work on, which will be the same name as your FCP project file. Make folders in there called Photos, Graphics, SFX, Music, whatever you need to stay logically organized. Your FCP project file and everything goes in there. This will be small and easy to back up to a DVD or something.
That's about it. Here's a link to my old monthly FCP column in Event DV where I talk about legacy FCP media management and workflow.
http://www.eventdv.net/Articles/Editorial/Tutorials/Cut-Lines-Editing-Workflow-in-Final-Cut-Pro-56036.htm