Well, as some of you know I play on the Glaphan server and I have already built three characters.
Now the questions I have refer to the three characters I have, so here it goes:

Assist: Lv.23
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What's the best way to build this character? FS or (I forgot what the other one was)

I have made mine somewhat a FS, I have maxed Heal out and had placed the buffs (from I think Lv.18 - 23) on lv.10 or 5, so I want to know the best place to train for this one.
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Magician: Lv.25
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I want to make him master Fire and Lightning magic is this the best strategy to go with? (referring to PvP and Monster wise)

And the main question for this character is...What's better: Psy or Ele?
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Merc: Lv.40
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Where's the best spot to train and get a lot of penya?

I can only really comment on the assist. First off, there is RingMaster, which is typically FS but not always, and then BillPoster, a battle specialist with the assist buffs. You can't really "somewhat" have an FS. Unless you're going to reskill and restat you have to pick a direction, either battle or FS. I have never heard of a battle assist maxing heal, so it sounds much more along the FS line. f you're going FS, you should find someone to help level you, because you won't be able to level alone. If you're going to go battle, you need different skills maxed. More info on what you want please.