Frankly, if you do not speak Korean well enough to function well in the society, there is no point in taking a Korean name. Koreans will tolerate you having a Korean name, but will be puzzled at the choice.
You should just stay with "화라하나" (hwarahana, closer in sound to your name) or "파라하나" (parahana, closer in writing, since Koreans often substitute P for F).
If you are worried that Koreans will not be able to pronounce your name, then shorten it and use "Hwara" or "Para". That will make more sense to Koreans than taking a Korean name.
[You could even separate your name and call yourself 화라 하나, ("Hwara Hana") so Hana looks like your last name. For what it's worth, Koreans know the name Grace--I looked at your other question--and Grace Hana sounds like a nice name, too.]
I am a permanent foreign resident of Korea.