Long Term Transition from Aperture

2. If I back these up for storage how do I also back up latest version of Aperture to use to access these photos?

3. Will I always be able to use Aperture in future OS's?

Make a bootable clone of the system drive on an external disk. This will backup the Aperture application and all support files it may need.

Apple announced, that Aperture will be supported during the life cycle of Yosemite, but made no guarantees for future systems. With a bootable clone you will be able to run Aperture and access old libraries, even if a future system upgrade should break the compatibility.

5. I assume from now on I should always store original photos and NOT depend on Application storage as it seems they can just become non functional at the whim or future of the software provider.

It is a good practice to always have backup copies of the original image files anyway. So export your originals to a backup drive.

4. If so I would back up libraries and start anew with Lightroom, PSE or PS cc or possible even Photos ( but unlikely). That way I could always pull out old photos and move forward with new software.

Photos can read the Aperture libraries. It will simple create migrated copies that will not need much additional space (see: Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support). So you can use Photos to access the libraries for exporting to other applications and simple edits. But Photos is not a professional tool. If you need professional photo software migrate your libraries to Capture One, Lightroom, perhaps the free digikam.