Why not just move the whole Library:
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.
As to your specific questions:
Tiff is an uncompressed format so the files are huge - 10 times larger or more. There may be an argument for using tiff if you expct to do lots and lots of additional editing. If not, then I'm not sure it's worth the extra space.
If you have the very latest version of iPhoto 11 then yes, that's an option in the export dialogue. Otherwise:
I've actually had this very same issue, and I didn't want to pay for any solutions - so I created a quick free Applescript that does the work for you.
Open the App, point it to your iPhoto Library, tell it where to save the photos, and go get a cup of coffee. Your photos will be copied *(not moved) to the destination folder, completly sorted with Folder names by Event.
I've posted this on my Mac Help Website: http://soniq.org/soniq/15749/iphoto-export-all-events-to-folders
I know it's an older thread, but this really did help me sort my 2000 events into nice clean folders.