In answer to both your questions regarding strings. It is a matter of
getting strings that have the correct amount of tension when in tune
and, for the bowed strings, a construction that responds well to
bowing. I don't think it makes any difference at all wound versus
unwound for the resonance strings as long as you get the correct
tension a pitch. The bowed strings are generally wound but there is
considerable controversy over whether or not the A string should be
wound or not (on a recent trip to Sweden very different views on this
were given to me one by several very reputable players and makers, I
think you just need to trust your own ear on this one).

See post my post 880 and follow the link to my string tension
calculator - you can use it to find unwound guitar strings that will
work as resonance strings. The Cello strings work an octave higher
because a the vibrating part of a nyckelharpa string is 400 mm and a
Cello string is 750 mm - so at slightly higher string tension the
nyckelharpa gets a note that is an octave higher (remember, you half a
string length you double the pitch).

--- In nyckelharpa@yahoogroups.com, "rlindau" <rlindx@...> wrote:
>
> Has anyone experience using plain strings for the lower resonance
strings?
>
> The sets I see (e.g., from ANA) all use wound strings for the lower
> resonance strings.
>
> I have problems with the resonance strings that run around my lower
> C-string peg - the winding on one has frayed due to contact with the
> C-string (which itself is wrapped around the peg, as you'd expect).
>
> It would seem that plain strings would be immune to this fraying
problem.
>
> A lesson is to loosen the resonance strings before turning the
> C-string peg (not that I do so often - usually the fine tuner
suffices).
>
> It doesn't seem possible to position the C-string winding so that the
> resonance strings don't contact it.
>
> I suppose another solution might be to put a cap over the C-string peg
> (something like a pen cap) so that the C-string winding is covered,
> and then run the resonance strings outside the cap. Such a solution
> wouldn't be very aesthetic, of course, and could lead to other
> problems (rattling, buzzing, misalignment of resonance strings with
> the slots in the nut, etc.).
>
> Thx, Rob Lindauer
>