If I revise my revision of a photo, will iPhoto make another copy so the database will have 3 copies of the photo, the original and both revisions?
No. Just the Master and the current revision.
If I dragged a revised photo to the desktop, went back into iPhoto and deleted the photo and then imported the photo from the desktop back into iPhoto, would iPhoto treat the imported photo as an original so there would only be one copy in the database, located in the Master's folder?
Yes.
But a couple of notes: If you drag the images to the desktop you'll lose a lot of metadata, best to export them.
It's a lot of work, introduces a lot of complexity to the workflow and that's how data gets lost.
but I may do fewer revisions to keep the library size manageable.
Don't worry about the size of the Library. If you're concerned about Disk Space you can run an iPhoto Library from an external disk:
Make sure the drive is formatted Mac OS Extended (Journaled)
1. Quit iPhoto
2. Copy the iPhoto Library from your Pictures Folder to the External Disk.
3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.
4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.
You can also run your iTunes, iMovies and Final Cut Pro X material from external disks.
Regards
TD