The Viola da mano is the Italian sister of the Spanisch vihuela. Unfortunately there is no surviving original so one has to work from iconography. With the vihuela we have the same problem. Just three original instruments survive, but each of them is very unusual and one of a kind. Looking at illustrations and looking at the repertoire one might get a better idea.
First of all there is the question of size. One original vihuela is very large (Musée Jacquemart-Andrée, Paris) and it would be impossible to play the relevant repertoire on it. One is quite small (Quito) and I wouldn't feel comfortable. The third, the 'Chambure' from Paris is about right - maybe for later. Most reconstructions I have seen are quite small. I always think about singers, since a good part of the repertoire are beautiful songs. I would be very uncomfortable to perform them very high.
I settled for Martin Shepherd's reconstruction after the famous illustration by Marcantonio Raimondi (c.1510), which is a good size instrument with a 68 cm scale. I play it as an instrument in E at 460 Hz with 6 x 2 courses, strung in pure gut. Build from cypress and quilted pear the instrument is simple and very beautiful at the same time.
The main repertoire is Luys Miláns 'El Maestro' from 1536 but a lot of Italian songs from the 16th century work quite well. I like the full rich sound I get from an instrument with double courses throughout. Courses 1-4 are in unison, courses 5 and six have octave stringing.