Q: iPhoto to Photos, iMovies, Moving from ext. Hard drives

I  have osx Yosemite 10.10.4 & iPhoto 9.6.1  on 16 GB 1600 MHz DDR3      When I move my iPhoto library to Photos , what happens to my iMovies?  I have my photos organized into events using a name for the titles. I also have a few Albums.  The photos in the events come from lots of different dates. It is the subject that is important to me.  My second question is this:  I have photos on my new iMac, photos on an ext. HD that I backed up to when my old Mac failed (thank goodness) and photos on another ext HD from my old PC. I want to get them all together.  Or should I wait until El Capitan comes out and Can I have 2 or 3 Libraries?  I read somewhere that photos were safer in either iPhotos or Photos rather than strays  elsewhere on the computer. Correct? I do not want to sync photos using iCloud. I move mine manually to my iMac and back up on a HD.

Thanks, Mary