I have imported a friends photos from his hard drive into LIghtroom 5 and all is good. One issue however is that MANY files have a double suffix, ie P100016.JPG.jpg or IMG-104.PSD.JPG. I haven;t the slightest idea how he did that but wonder about advice to fix. Also, a folder in his Photos is called Adobe Bridge Cache and it contains thousands of photos when viewed from Lightroom, yet that same folder when viewed from Bridge, says nothing to display. All are also visible when viewed through Explorer. I have a mess on my hands and am unsure how to clean it up.
In general, you wouldn't want a Cache folder to be imported into Lightroom, so if I were you, I would simply delete the photos in this folder from Lightroom (but do not delete from the hard disk)
With regards to the files with double suffixes, if everything is working properly, I would leave it alone. Don't fix it if it ain't broke.