Yea, Goblins are the most warlike of the races, they very often follow demons as their lords ingame, as well as kidnapping and brainwashing children of other civilizations to join their culture. Sometimes you can even get goblin civs without any goblins, because they all died and now have an elf king or something because of this. However, ingame, all the races wage war indiscriminatly against each other and hold no common spite agains goblins. I think Toady is working on the game mechanics for that still, but right now they seem to wage war mostly for fun. Goblins are the most warlike though, that is very much true.

As for the size, just remember to put stuff there that is for the map, so to speak. If its not intresting or gives anything to the map as a whole, then I'd drop it.
The fine line between cluttered and detailed.