Hi,
lots of questions, so will try to answer some of them.
Physio Assistant: you won't need any qualification for this, i.e. you don't need to contact the Physiotherapy Board. Same for Health Care Assistant. It is possible to get short term jobs as Physio Assistrant, especially in summer, as others will be on holiday ... that is... our summer, I mean. So the time from December to February. Is that what you understand as summer???
Where to start: contact Immigration in regards to what kind of permit you need. You might be able to work on a working holiday visa, depending on your age.
Working in New Zealand
Recommend to check this website.
For jobs, I would contact the Allied Health departments of the DHBs directly. Those short term jobs are hardly ever advertised. So, you could google the DHBs.
District Health Boards Contents
Hope this helps,
regards,
Fyzzio