Instead of answering directly, I'll give you the history of the dynamics of my tank. Unfortunately, it involes the death of two gouramis, but you may find it helpful. I initially started with two small opalines: a blue and a gold. I thought both were females (that was my intention), but the blue turned out to be a male. The blue quickly took to bullying the gold, and chasing her away from any food in the blue's staked out half of the tank. The blue was initially slightly bigger than the gold, but they were both small. Over a couple of months, but grew fairly good sized. I knew I wanted to add some pearls, but I had similar concerns as I had also read and heard that pearls are much more passive. I selected three pearls total: a male slightly smaller than the blue, and two females slightly larger. Interestingly, the first thing that happened was the blue mostly ignored the pearls unless they crossed over into his territory during feeding time. But the gold, who was about half their size, instantly took to chasing them all over the tank. It was funny in a way--almost like she said "I'm sick of being picked on, so now it's somebody else's turn!" Anyhow, after a couple of weeks when the pearls settled in, this stopped. I think the size difference helped. I pretty much had gourami equilibrium. Then suddenly, I found the gold dead, wedged in between the back glass and a flower pot. I don't think anyone killed her--she was stuck back there and couldn't get out. I don't know if she was chased or if she was going after some food or what, but I just could not find her for a couple of days, and then discovered her back there after I noticed my loaches constantly trying to get back there to get at whatever was back there. Anyhow, I think her death was unrelated, but I wanted to mention the whole tank dynamic with her in there. Shortly after that, one of the females died also. The whole batch of pearls was fairly new at the lfs when I bought them, so it may have just been a bad or stressed fish that looked healthy and didn't make it. But I'm also not ruling out the possibility that the other pearls two killed her. They have not tried to spawn, but otherwise act like a pair. So there may have been some aggression. Not ruling it out. Anyway, the blue tries getting a little cocky at times with the pearls, but it is not an issue. Because of the tank size, the female pearl will just swim out of the blue's territory, and that ends that. The male pearl won't have any of it, and frequently chases the blue whenever the blue tries being silly. So, long, rambling story, but there you have it. My tank balance is fine now, but I probably would not add anymore gouramis. Multiple female opalines might be okay if no male is present. But with a male, I am afraid it would bring out aggression. Similarly, I do not want to add anymore pearls in case either my pair kills them, or in case it might otherwise bring out more aggression on the part of the male pearl. I seem to have a very good balance now for the size tank I have.
