You can get into Tainan Taiwan via Kaoshiung Airport via Kuala Lumpur Malaysia. If you're in Taipei you can take the high speed railway from Taipei. The train prices are no expensive. I would recommend getting your sim cards at the airport or in Taipei city. There are pretty good plans that offer unlimited sim card data at 4g speeds. I paid 450 nt for 8 days with Taiwan mobile. A sim card is key to getting the most out of Tainan or Taiwan in general.