Welcome jpeck.
I have a 1931 National Duolian, w/ orig cone.(so Bob Brozman tells me).
Great guitars, the real deal.
Be careful with the neck and the cone.
They can develop a bend where the neck joins the body if you have too much tension, especially in warmer climates.
I recently moved from the top of a Mountain to the sub-tropics, and noticed a slight rise at the 12th fret, on an otherwise perfect neck.
I had been using a custom gauge .013>.056 tuned to open E. (Too much tension, silly me).
I dropped the tuning down to open D, and imediatly noticed an improvement in tone and sustain. Seems too much tension "chokes" the cone.
The custom gauge I now use is .015 .019 .022w .030w .040w .056w
in open D tuning (vestapol) and its great!
I customised this gauge to even out the tension of vestapol tuning.
You can't buy them, you have to make em up yourself from singles.
(This may not suit you if you use a lot of different tunings on the guitar).
Below is a link to a tension calculator.
To answer your question depends on what tuning you are using, but I'd be reluctant to put Dobro (.016 < .060) stings on the National.
No tricks to the classical style tuners, they are a pain in the arse.
I put the first wind under so as to lock them in, and always have the winds finish on the outside relative to where the hole in the barrel is.
Good luck, hope I've helped.
www.mcdonaldstrings.com/stringxxiii.html