At the Airport
Assuming (and fingers crossed!) that nothing goes wrong with your visa and luggage, you can first get a metro card from the information desk, which can save you the hassle of doing so later. Depending on your situation, it’s most likely you’ll want to buy and set up some connection to the internet before leaving the safety of the airport! Although there a couple of mobile network stalls dotted around (this guide is pretty great at highlighting locations) most recommended is ChungHua 中華電信since coverage is also great for travelling outside of Taipei!