I don't think Linux lets it's disk get fragmented. I think they use the same on-the-fly defragmentation that OSX does.

The reason that you should defragment before changing windows stuff around is because Windows defragmenter compacts everything to one end of the disk, this means what you are resizing is empty and it doesn't have to move anything. You don't have to do it, a good repartitioner should copy the files that it needs to, it just makes it faster.

I'm not sure how you backed up everything on your external, but I would make sure that you back up the files, not the file system. ie, just those files you need, don't make an image of the whole disk, that could cause problems.