Not sure where to start. Christchurch will probably seem small, quiet and cold compared to Indonesia, but it's large enough to be interesting, and the countryside is pretty stunning in places. Not particularly unsafe unless you are in the wrong places at the wrong times. For students here (like visiting PhD students I've known) I'd say about 150000 NZD is enough to be comfortable. Less than about 12000 NZD would be difficult.
A lot more Asian people here than there used to be, but I don't see a lot of Indonesians. There are Thai and Sri Lankan monasteries, but the largest Asian presence is Chinese.
What sort of internship is this?
I'd be happy to answer more detailed questions by PM.