Manage iPhoto event from Lightroom
While it is far from an ideal solution, when I want to put the Lightroom-created JPEGs in iPhoto, I've been using the following to solve #1:


Publish to a Hard Drive folder from Lightroom, each folder named according to the events I want them to have in iPhoto
Uncheck the "Copy Items to the iPhoto Library" box in iPhoto's Preferences>Advanced menu
Import the folders to iPhoto


This will import these pictures by reference only; all the photos stay in their existing folder. (I usually re-check the box afterwards, so later pictures from sources other than Lightroom are actually copied). But you can set all the usually iPhoto metadata, reorganize into different events, browse thumbnails, etc. 

If you modify anything in Lightroom, and republish the changes, those changes will be visible immediately when you open the picture in iPhoto. Note however, that unfortunately iPhoto does not update the thumbnail. And iPhoto uses the thumbnail for the zooming-in animation. So not only when you view it in the event display, but for a moment in the zoom-in animation, you will see the original version. But on the plus side, any metadata changes that you make will be preserved, because iPhoto stores these in the database. Only the image is external. 

Also, since I don't like having another folder outside of the iPhoto database, I actually have Lightroom publish to a folder that is within the iPhoto database package. iPhoto doesn't delete anything in there that it didn't originally create, as far as I can tell. I have tried to use the "repair library" option to see if it can pull in the files (it claims to be able to recover orphans), but no luck there.

Unfortunately, iPhoto does not check when the files are removed. So it doesn't solve #2. It sort of solves #3, in that there is no additional copy.

Anyways, like I said, it's a very imperfect solution, but I've found it to work reasonably well for myself, and it's the best that I've come up with. There is a plugin that purports to be a Lightroom Publish Service for iPhoto, but it doesn't work at all (it's basically an export; it doesn't update photos). 

Best of luck!