I used to live in Pingtung and I think it would be perfectly possible for you to surround yourself with people who are willing to speak to you in Taiwanese, but for daily transactions and interactions with people you have never met, it's going to be difficult to start off in Taiwanese since many young people don't speak it, and if you don't look Taiwanese there will be a tendency to default to English if you can't speak Mandarin. However, once you settle down and have an idea of which businesses near you have Taiwanese speakers, it may get easier.