The slate (if that's what it is) does look better, and more stable. Good thinking.
The fish you have will appreciate the additions, absolutely; there is an interaction between fish in such species (sometimes very entertaining for us, as well as necessary for them), as well as the plain "security" aspect of groups.
The butterfly does indeed sound like the African Butterfly fish, Pantodon buchholzi. Photo attached for reference. Very interesting "pre-historic" looking fish. I've had a pair many years ago. They do best in pairs and they interact a lot. Males have a split in the anal fin very distinctive; the first few rays are much longer than the rest, with a bit of a split between the first group and the rest. The photo attached is a male. The female anal fin is complete and rounded, no extended rays. Although they are reportedly easy to spawn, mine didn't; but then that was 20 years ago and I was new to much of this. There was an article on this fish in one of the recent issues of either TFH or AFI, I could track it down if you're interested. They need soft, acidic water, and plants, especially floating plants; they remain motionless among the plants, but spring into action to feed. And they will interact, play or spawning behaviours, regularly. They also jump, very well. The tank must be well covered, no escape holes. And obviously no small fish in the tank, they are avid predators of anything that gets near the surface; the mouth extends from the tip at the nostrils down to a point well back of the eye, so it is large. Crickets, mealworms are good food, plus beetles. Mine readily accepted chunky prepared foods, dry and frozen, frozen squid a favourite. Anything that will float.