We all have different ways of storing and cataloguing our photos. I can't say my method is necessarily good or foolproof, but has I think a reasonable level of security against data loss. I am a firm believer in triple redundancy,
Because I am paranoid about software and files suddenly disappearing, discs crashing, and even possible theft of hardware, I stock all my photos in folders, one (or occasionally more) per day they were taken (to keep them in order the folder names all start with yyyy_mm_dd followed by the name and place of the occasion, so easily searchable). THREE copies on different external hard discs, one of which is on my local area network. Each copy is referenced in one of two versions of iPhoto, for use on different generations of machine - my wife's MacBook Pro under Mountain Lion and my MacBook Pro Retina under Yosemite. Aperture can also read the libraries when I need its characteristics. So NO iPhoto or Aperture library actually contains any photos, only references, faces and location information, and occasionally modified versions of photos, which I copy back with a new file name systematically to the photo folders. Synchronisation is not really a problem as all is sequential in time - I load photos from our camera cards onto one hard disc, rotate those that need it, then just copy them across to the other discs.
I now have a new library for Apple's Photos - I copied one of my iPhoto libraries and let Photos convert that copy - so my photos themselves remain untouched. Just as well, given he amount of information Photos has left out - for example all the file names have disappeared, I just have bare photos, with a blank space underneath to put in a title manually. What on earth Apple were thinking of when they rolled out Photos in that state is beyond my comprehension.
Ultimately, if a new version of OS X no longer lets me use iPhoto or Aperture and Apple hasn't drastically improved Photos to the point where it may become useable, I shall either have to keep an old version of OS X purely to use no-longer-allowed software or migrate everything to Lightroom or something else.