i've got a retirement visa. if i took a teaching job would i have to give up my retirement visa for a work permit? if so i'll forget teaching. not worth it.

Yes you would have to give up your extension of stay based upon retiremnett it is not a visa.

You cannot get a work permit with a retirement extension.

Would depend on where you live. A year ago Sunbelt reported they were able to get a Work permit for someone who had an extension of stay based on reitrement. So inquire at your labour office it they accept it or not.

The thing is you can always go back to retirement later if you want to quit the job. As long as you meet the requirements for the class of extension you want it is not that hard to start again. You do it every year in any case.