Hello Kim,
I play a symphony made by Chris Allen. It has one drone string, two melody strings and one trumpet string and it is chromatic over 2 octaves. I am very content of this instrument because of the fine tone and its reliability, it works perfectly. It is more quiet than larger hurdies, making it a fine instrument for accompaying a singer. However, in a mix of instruments it can be heard better than I would expect. I have no experience with amplification of the symphony. I have tuned the drone to d with a capo to g, the melody strings to c' (very useful for medieval modal music) and the trumpet to d'.
I would strongly advice you to choose an instrument with a trumpet string. Then you can decide where to use it. The first appearance of a trumpet string on a hurdy gurdy in pictures is in "the garden of earthly delights"of Jeroen Bosch of about 1500, as you will know probably, but in late medieval instruments, often a facility for supplying a rattling to the sound is incorporated, so I think that more primitive predecessors of the trumpet string might have been used earlier, and, anyhow, I think that using a trumpet string in some medieval music may be appropriate, so I use it when I like it. Although I have only restricted capabilities on the trumpet string, it makes my playing more attractive for most listeners.
I also play the Aachen, a hurdy gurdy that has been made by Chris Allen especially for medieval music. This might be an interesting option for you as well. It has a beautiful sound, somewhat louder than the symphony and it works fine. I have 2 drones (G and d'), two melody strings (in principle also in c' as on my symphony but with a very useful lower extension to a) and one trumpet string in a with capo to d'. In fact I have 3 more capos, but I seldom use these.
You can hear it on
http://www.youtube.com/watch?v=nR_R3FhkQ4Ewith explanations and demonstrations on
http://www.youtube.com/watch?v=K0J41t_XV5g
http://www.youtube.com/watch?v=9j1KmZuU-dwhttp://www.youtube.com/watch?v=1ciEmQOZlAshttp://www.youtube.com/watch?v=_hAvGYyrKCY
Good luck with finding a suitable hurdy gurdy!
Ernic