Hey there! I'm Ivy on Discord, and we've already bumped into each other x3. So, here's my little welcome to you! As for guild suggestions, I may be rather biased as I am the GM of Fairy Tail, but I assure you we're rather different from the anime version. For dark guilds, I would love to point you in the direction of Basilisk Fang, which is something like the terrorist guild, going against the Magic Council.
Feel free to shoot me any questions, or want to rp /o/