I've had external drives lose data mainly because of the junky interfaces/chipsets used in some caddys and external hard drive enclosures and usually during boot up or shut down. I too would recommend a fat internal drive for storing all models, textures, references, vdbs, hdr and things in an assets folder. If you want to, get an external drive and do a one way sync between them once a month or so as a backup.
As a contingency, I'd look at something like EaseUS Data Recovery Wizard or similar for recovering files that were lost from a screwed partition/drive. For files that were deleted on working drives I try to remember to use Recuva (free version). There are also online backup options like Crashplan (I use), Backblaze or others.