1) iPhoto-Preferences-events, uncheck "imported events from finder" -- is supposed to prevent autosplitting folders dragged in or imported. Not sure I've done this, so can't verify it works as advertised.
2) yes: iPhoto-preferences-advanced uncheck "copy items to the iPhoto library."
3) My $.02 -- You can organize photos by "album," AND events, so may as well use two different organizing schemes (and even better, when you import the folder, add a keyword to all the photos (select all, command-k), then you can change around the scheme and still come back to your original folder names)