Honestly, I have no idea why I'm trying this. This is mainly for staff; Comment with current server issues and I will come up with a solution to each of them. It might not be the right way, but I've got a pretty good chance since I'm good in this field.
Maybe you should eat a walrus. That's just how signs are. No plugin (as far as I'm aware of) can change the character limit on them. Color codes are a privilege, not a necessity, though I do share your view: it's annoying. Neither do I, because I'm 16 and I don't have a life besides these forums and photoshop. Better to wait it out and see if they fix themselves, aye? /coop kick & /trust are part of the same plugin, so I'll answer both together: The only reason they wouldn't be working properly is because of mistakes made while changing the plugin, or because it's interfering with another one. For now, try not to use them. Why do you have a Mac?
Did a small amount of research and came up with this; On a Mac (apparently because of an OS update), pressing 'enter' on a sign to go down a line also adds a space. So, every time you hit enter, press backspace to get rid of it, or it'll be messed up. You may also need to download a new Java version, if that doesn't work. Downgrading to Minecraft 1.8.4 might help, also, since it seems to be the most stable version out.
I Don't own a Mac, but many players on the servers do. Answering a Question with a question is not rather helpful. =P But, as for the real answer, Much more informative and helpful.