I have been to Hornbill and its amazing. My suggestion will be that go towards the end of the festival. Its full of culture, performances, food, happy faces all around. You can spend 2days in the festival which takes place in Kisama village and then also cover Imphal: Loktak and Kangla if you wish to.. You will get few Dzukou travellers too but trust me Dzukou is best to be visited in Jul-Sep.
It is absolutely safe to travel solo there, even for a lady. It is a great festival, lots of cultural extravaganza.Yes it is safe to travel solo but make sure you are staying at Nagaland Tourism approved Hotel. (You can find it Nagaland tourism’s website)