How big of a tank will I need for these? How much do they cost? How many can I keep together? What would be good tankmates? What are their ph requirements? And how do you think I could wean these guys into pellets?

not really a big tank..but these guys prefer calm water..it will be quite hard to train them with pellets..but i've seen people who has done that.

before my huge down grade i have 17 in a tank but it was a 6' 3' tank and they hunted with eachother and schooled some some times. they need floating plants to feel safe.

Umm, how many would a 3.5x1 1/2x2 foot tank be able to hold? And what are some suggested tankmates, as I am considering the small Snakeheads for this.

You could easily keep at least 3 in that tank. I trained mine to eat flakes and pellets very quickly. I just put them in and moved them around to make the pellet look alive, so the butterflyfish eventually started taking them without movement. It eats flakes as well.
Good tankmates would be basically any non aggressive fish that is about the same size or larger and aren't surface dwellers.

So, would the smaller snakeheads, Hujetas or Needlefish, and a peacock eel work as tankmates? Also, what sort of PH and water hardness should I be aiming for?

well make it a african theam tank get some small bichirs like sengals and dels and palmas polli and thoes types. and get a big school of congo tetras it would look sweet.

That sounds like a real nice setup!!!

Thanks for the suggestions (Adds Bichirs to list of tankmates )
However, I'd still like an answer to my question.

In my experience, these fish are pretty flexible for pH. I currently have one in brackish water, and I have heard of them being kept in soft, acidic water too.

So would the fish I'm planning to keep with it in the above post be good or bad tankmates?

I'm not sure about the snakeheads, they tend to be aggressive and get fairly large. Butterflyfish stay around 4-6 inches. the needlefish should be fine for a while. and the peacock eel would also make a good tankmate since it inhabits the bottom part of the tank.

So, the gachua, bleheri, and orientalis wouldn't work?

And what do you mean by the needlefish being fine for a while? Will they get larger?

Another question.

Would Pikeheads (Luciocephalus), African Labyrinth Fish, Large Bettas (Macrostoma and such), and African Mudfish/Hingemouths work as tankmates?

I can't say from experience that any of those will or won't work but I kept my Butterflies with many different Cichlids, Tetras, Bichirs, a Tiretrack Eel, 8" Kissing Gourami, 8" Snakeskin Gourami, and various Catfish. One thing I can't stress enough is KEEP THE TANK COVERED SECURELY or you will lose your Butterflies. Because they, like their much larger cousins the Arowanas, are strict surface dwellers, they're incredibly skittish. The slightest little thing will spook them. They jump and end up on the floor. The tank mine were in is tightly covered because of the Eels and Bichirs. But my pair of Butterflies managed to jump through a 1/2 opening around the one filter intake any way.

I had 2 a long time ago. They would not eat pellets. The only thing they would eat (aside from guppies) was krill. They seemed to love it

Ok. So how big do most of them get in captivity? I've heard 4-6 inches, but what size have most of the people who kept them have they grown to?

Mine grew to about four or five inches. Both males and females seemed to grow at about the same rate to the same size. They grow pretty quick depending on how often and how much they're fed.

Mine got onto pellets quite easily, Butterflys don't do well with other surface dwellers. The rule I use for butterflys is:
Anything that is really agressive (like cichlids) and/or has a big mouth and/or lives at the surface and/or is a fin nipper, will not mix with African Butterflys. Some of my reccomended tankmates would be: Rope fish, Knife fish, and small to mid-sise catfish.Don't try the pike-head they are waaaay too agressive. P.H. isn't that important as long as it is not too hard or too soft. Good Luck