If you have T-Money card, then no need to buy Hanaro or Mybi. And even if you don't have T-Money card, you had better buy T-Money card because you can use it at the cities in your travel list (except for Hwacheon : According to T-Money and Mybi sites, it's not in the service list).

Of course Mybi card is also available in Busan, Gyeongju, Jeonju, Seoul, but your first stop in korea would be Incheon or Seoul or Gyeonggi (T-Money card is mainly used) so it's better to buy T-Money card and use it at Busan, Gyeongju, Jeonju.

The problem is that it's hard to find the recharging places where Mybi card is mainly used like Busan, Gyeongju, Jeonju, but there're some ways even though it's still inconvenient a little :
- Shinhan Bank ATMs which have Transportation Card Recharging Module
- Post Office ATMs which have Transportation Card Recharging Module

I think Gyeongchun Line is the easiest way, but choose is yourself :
https://www.namisum.com/_ver01/_bbs_iw2000/?link_code=090103

The weather of Incheon Airport ( Incheon Jungu ), and Mid-term forecast.