1) Even though it's what Kato wanted, Kato wasn't the only scenario planner so just because he wants it that, doesn't mean it is.
Surely, they must have thought about the outrage or odd continuity by having the whole story just finish with Kid and Serge looking between worlds for each other.
Magus was mentioned in the game that he would find Kid one day. Kid is looking for Serge, so she doesn't care about finding her brother? Somewhere there, we must have missed something.
That ending soliloquy doesn't state anywhere "Serge", or in fact who will be looked for.
Furthermore, Kato said that Kid would look for Serge. This brings about two more possibilities.
a) Kid and Serge do not end up together in the ending of Another World because Serge and Leena get married instead so Kid looks in another dimension for him.
b) Kato is fluctuating between ideas and canon because Kid and Schala become one, and Schala=/=Kid so whose looking for who?
c) Theres the same chance that this time Schala is looking for Janus in another world just as much as she is looking for Serge.
2) I always thought her name was sounded more like "Har-lae" or "Harley". Pay attention to the Dragon God song, and you can hear something that sounds like "Har-lae" in those strange, hypnotic lyrics.
It might mean something in Japanese, or in some other language regarding the moon.
On the topic of Tsukiyomi, it literally means "Moon reading". Tsuki, especially in Kanji means "Moon". Yomi stems from Yomimasu - to read.
The English version's name fails to live up to what Harle really is, a fragment of the Black Moon in some connection.
3) As Chrono'99 stated, Kato and Honeywood worked together on the English names. However, I think that leaves also detremented the English versions character development, or story. Like with Harle, you know she has something to do with the Black Moon in the Japanese Version. In the English Version, you only find out that she's the Dragon of the Black Moon near the end of the game, and the only other hint would be with her Lunateric tech.