I did an ocarina one a while back. I was planning on remaking it soon. Basically I planned on recording 3 different samples, as the reclists I was using had 5 mora, 7 mora, 6 mora samples. Just to better give the sorry of transitions. Then just go into the oto in a .txt editor like notepad and edit the names of the samples (Bababibabubeba) to 7mora.wav.
Then just edit one of each, copy and paste into the oto again, and Bam! Instrumental UTAU.
As far as instrument wise, I can basically only give help with ones with mouth pieces...
Breath REALLY deep and push out air as though you were saying 'tu'. It helps with clarity.
I hope I was able to help. If you have any more questions, feel free to ask. ^-^