Where to start? 5-String Paul Pyle Mountain Dulcimer

I've had this dulcimer for over 13 years.  I've tinkered around with strumming and chording.  I have not accomplished much, but that is because I haven't dedicated much to it.

I've got a few questions:

Tuning?  What should I tune this 5-string to?  Looks like I have 2 strings for Melody, 2 strings for middle set and a single Bass (pardon my ignorance on now knowing all the correct names.)  For learning purposes, what would be the best tuning to use?  DAD?  

Strings?  What would be a good diameter string to use for each set?  The length from Nut to Bridge is 28".  

When looking at information on the interwebz, I find references to 3 string and 4 string, but nothing much at all about 5-string MD's.  Is there anything I really need to know to learn to play this properly?  Is this not the best way to begin learning?  Would a 3-string be a better starting point?

Thank you so very much!!!!

Claud