How to Remove Duplicates/Other Images from Large Library?

iPhoto 11 (9.5.1)

Mac OS X: 10.7.1

Situation: A couple months ago my wife imported the entire hard drive into iPhoto on her machine by accident. There are now 72,000+ photos, many of them duplicates and a lot of them thumbnails, cache images and random pictures and movies. I am guessing the original number was around 5,000. There is no backup of the original database.

Goal: Get database back to original (as close as possible) and remove all duplicate photos.

What I've tried: I first tried removing a lot of the images which were not by creating a smart albums based on specific information (e.g., filenames = ".gif" to remove Internet images, No EXIF data to remove thumbnails and other files, etc.) This was a great start as I was able to remove around 50,000 photos.

But then this caused a major problem when I selected "Empty iPhoto Trash". I let it tun for 24 hours but it never finished and had to force quit. This corrupted the database (I do have a backup of the 72,000+ photo database) and have basically now started from scratch again.

So now I have three questions:

1) Is there a way to create a smart album which is based on the size of the photo? (e.g., I only want photos which are greater than 800x800)

2) What is the best way to remove a large number of photos?

3) And then, once that is complete, how do I remove the duplicate photos?