I have had three peacock eels at one time in the past and bought them at about four to five inches. I was told to feed them guppy fry and ended up raising a bunch of guppies in the same tank. I had the eels for about 6 months before I changed over to cichlids and traded them in. They grew pretty slow in my experience.
I have seen the fire eels get pretty large, but not a peacock eel yet. That is not to say that they dont get as big, just never seen one. In a video of the fire eel, it was blood worms from the person's hand. I dont think they are especially mean in any terms (again, not 100% sure on that though), but any fish that can fit another into its mouth is more than likely going to take the meal. Mine really loved blood worms and brine/mysis shrimp though which was hard to keep around in the tank because most other fish love it too. I would put a fozen cube in a little tree stump decor so that it was out of sight, out of mind to the other fish and wouldn't float to the top of the tank. Then it would melt and the eels would get it. I also bought a little system of LED lights that I put in the tank so that I could see them more often since they are very much nocturnal.
These eels are not true eels though so they dont get to the sizes or have the teeth of a Moray eel, for example. Also, you shouldnt keep any of them unless you have a very fine substrate since they all like to bury themselves in it and they spend a lot of time this way. They are scaleless fish so salt shouldnt be used at all or in very very small amounts. If the substrate is too rough, they can scratch themselves on it or hurt their eyes, which they dont really need all that much apparently, but this can all lead to secondary infections and cause big problems. If you notice that your eel is not buried or spends alot of time hiding in a fake plant (real plants are not a good idea since they will up root them while moving around in the substrate), there is probrably an issue with another bottom dwelling fish like a pleco, loach, or catfish stressing it out. I found that they are great at picking up food that has falled to the substrate so other bottom dwellers are basically not needed and it would be better to avoid them and scrape algea by hand if need be. Last, but not least, you have to be VERY careful when you are vaccuming out the substrate so that you do not hurt one when it is buried which I happened to do to one of my eels and unfortunately must have broke its back and it did not survive. :sad:
Don't have any experience with the bichir though.