Unless they've changed, it's only a soprano model. Given the nature and design of a sitar, I think a longer scale is probably much more appropriate. I played a sitar back in my 20s, and wish I had kept up with it (as well as kept the instrument, which was a beauty):
The buzzing/droning sound of the sitar derives from three main features: the sympathetic strings, which vibrate in tune to notes played on the main strings, the drone strings which are struck during play to accentuate a phrase, and the bridges, which have a flat surface that the strings touch when struck (which creates the buzzing sound).
Nylon strings won't work for this because of this bridge. They don't buzz properly and the material tends to dampen the energy. Has to be metal. I'm sure you'd wear nylon strings apart pretty quickly, too.
There are secondary (sympathetic) strings underneath. Six from the pictures. Not sure how they are tuned but likely four are an octave apart from the main strings. There are no drone strings, however.
The sympathetic strings have their own, similar bridge, underneath the main strings. You don't actually play these strings, just leave them to vibrate on their own. They need to be in proper tune else they won't vibrate.
Strings are high and not pressed against a fretboard, but rather against the frets which are arched pieces of metal that stand high above the neck. This means new callouses. Frets are strapped on, and moveable, not fixed.
Check the
Chandrtakantha site for more details on standard sitars. It looks like an interesting experiement, but so far the videos haven't impressed me. The tonal depth of a sitar is missing - that may be just the recordings, but may also be the small size of the resonator.
Several years ago, I tried various homemade bridge extensions under the strings of my guitars to get this sort of effect. Didn't sound too bad. I've often thought I could do better with a 3 or 4-string cigar box guitar or even a dulcimer. I did tinker a bit with this idea on my Strumstick, but didn't quite make the right kind of extension and sold it before I found one.