Questions about the Korean dubbed Aria series and OPs
I don't have sources to cite for all of these, I can maybe come back later and add them if I find them.


The reasons songs aren't dubbed are because of the cost of a singer and the additional costs of licensing the rights to re-record the song. There's licensing the rights to simply translate the lyrics but redubbing the vocals would be a completely different recording. Re-recording often happens when the localized dubbed version is intended to be released, so people can buy the localized dub opening theme music (full length versions, etc).
As for the katakana missing from the title screen, this is probably entirely an artistic decision. The original 3 katakana fits nicely between the 4 western letters, but in the Korean version, there are only 3 Korean characters which only provides 2 slots for the dots inbetween the characters. They probably decided to make all the dots the same for both the English and Korean for consistency, instead of making the dots in the English word filled in with katakana and have them changed to just dots when the title screen transitioned to Korean. Additionally, they probably didn't want to people to think the katakana was really tiny Korean characters.
The director credits for localized versions usually mean the director of the acting. There's a director for the voice acting for a localized dub, just like there's a director for the voice acting in the original Japanese. And just like the recorded acting needs to be edited, mixed, engineered, etc into the final sound tracks in the original Japanese, the same thing needs to happen for a localized dub. I'm guessing that's what the director and editor credits are for.