Lawful Goods usually mean well, but they're often humongous squares. I doubt that the Justice guys would be a major problem, as in "have to fight them even though Julie reeeeaaallydoesn't want to", but I'm positive that they're still going to be a major pain in the collective butts of Julie's party. Who wants to bet that the first spell Harvey casts or casted after talking with Julie was Sending? I sure am.
What's the demon that took over Silverfronds Castle
How powerful is the one piece of the Magicant I recovered?
How many pieces would I need to gather to banish said demon?
Well they can't grant any wishes until they're reunited, but we did see it do a weird true-seeing effect sort of deal on Emily when she seized it at the end of book 2. Even still, she doesn't have the Magicant Piece itself right now anyway (She apparently hid it in her own dreamworld) so it doesn't matter that much.
Hey, I know! Emily can ask the demon for a wish and get the Magicant that way. Save a lot of time and trouble for everyone.
Demon wishes aren't any more powerful than the Level 9 spell, and they're even more liable to go awry than wishing the conventional magic way. The conventional magic way wouldn't work either since artifacts are more usually tied with epic magic, it's beyond even Wish.
Hmmm... I get that the Magicant is a major artifact, powerful beyond any form of mortal magic, but how in the flippin' three hells is it stronger than the gods themselves? I mean, Quizma probably used to be the god of Chaos("used to" because she got kicked out after the Magicant fiasco), so it makes sense that she'd have been a Greater God... But she was only one god, and there had to be at least five or six others(the three Good gods, Sarbek, the then-ruler of the Great Empirically Awesome Rule System, maybe Tlondal and/or the former CE ruler of demons...).