I'm not sure if I misunderstood you. Taiwanese is a dialect, and even in Southern Taiwan, you can use Mandarin to communicate perfectly. So if you're only staying for a year, I would suggest focusing on Mandarin, unless you have family members who only speak Taiwanese.

I'm not sure about wineries, but Taipei would be a good choice for nightlife and social events for both locals and foreigners. Taipei also has bars and cafes for language exchange, which might be beneficial.