Also what are my options for when my hard drive quickly fills up?
You could relocate some of your referenced originals to an external drive - for example the originals for older projects that no longer need editing. Then you can save space and still work on the newer projects, even if the external is not connected.
I wonder why aperture has been running fine for over 18months until now?
If a transmission error corrupted the library that may occur randomly.
But the same symptoms can be caused by importing images or videos that cannot be processed. Can you start Aperture, if you launch it with the Shift key held down, while clicking the Aperture icon? That will defer the generation of previews.
If Aperture does not hang in this mode, it usually means, that you imported someting that Aperture cannot process.