(am currently in the military)

the website used for enlisting is an absolute clusterfuck of korean that was stupidly convoluted i feel you there

as for the level of korean needed, you'll learn as you go. a lot of the words used in the military are military specific that even normal koreans don't use. get used to "-다나까" which is like the ultimate 존댓말 form that you need to use to your superiors! it's frowned upon to end your sentences with -요 to anyone ranked higher than you.

ex) i just went to the bathroom 화장실 갔다왔어요 > 화장실 갔다왔습니다

have you eaten yet? 식사하셨어요? > 식사하셨습니까?

i honestly wouldn't count on getting into katusa bc it's completely random (though it would be ideal)

once you get to your base and you explain your situation, they'll understand that you need extra help w communication and what not so if they're nice they'll kinda guide you along the way

a lot of my friends can't speak korean that well but they're doing/did just fine so don't worry too much!

just try to use korean as much as possible in your day to day routine from now on. reply to your mom in korean, if you don't know how to say it then ask her how. journal entries so that you get used to expressing your thoughts and opinions in korean.

good luck! :)