Am I on the right track with regards to how DB_File via 'tie' works and the merits of DB_File as a method storing and retrieving data?

You have it working, so all of the syntax is correct. As for the usage of DB_File, it seems to me you have found it's exact usefulness. I tend to work in RDMS's, so i don't normally use DB_File, but you seem to have it's number ... keep it up.