Bluesman,YOU'RE PAYING SIXTY DOLLARS FOR AUTOHARP STRINGS?
We can make this easy, get a hold of an Elderly Catalog (www.elderly.com). They're $32. a complete set (plus about $4. S&H). You'll need a set of A's for the older one and possibly for your 15-bar, depending on the type of end piece you've got. A's are loop ends for older models with endpins, B's are balls for slot bridges.
As for single string picking, you'll need to learn "choking" on an autoharp. Example: a C chord gives you the notes C, G,and E. While holding the C chord bar down drop the Am chord bar. You now have only C and E strings available to play. Add the F chord bar and you only have C strings left. You can also do a hammer-off effect by lifting off a second chord bar half way through a strum or single sting picking to pick up the second, third or fourth notes (7ths) at the upper or lower register (depending on the direction you're going). Try this on a C7 to Am back to C7 on the bridge of "The First Time" by Ewan McCall or a Dm to D7 to G7 in "Laura's Theme" (Someday My Love) using the thimble tremelo I described earlier.
I keep telling people that think autoharps are too simple, that when it comes to autoharps, "Simple is, as simple thinks."