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The white BoP has notoriously fragile leaves. You can put it in a place where it gets more light, to give it more energy to push it's leaves out all the way. You can also wipe along the edge where the new leaf is "glued" to itself. Use a little warm water, or (better still) some spit on the end of the finger. You can get the "glue" to come loose, so that the leaf can open evenly, without getting caught part way, causing the leaf to tear.

Here's some general information on transplanting bushes: https://www.gardeningknowhow.com/ornamental/trees/tgen/transplanting-trees.htm
You might want to prune the foliage very gently when you move it, and make sure it has plenty of water while establishing itself in its new location.

Caesalpinia is apparently quite easy to grow from seed. This article is about a slightly different species than red mexican bird of paradise, but I think the process would be the same. http://www2.hawaii.edu/~eherring/hawnprop/cae-kava.htm

Mexican bird of paradise is a tropical plant, so the farther north you go, the less happy it becomes. It is considered a "returning perenial" in zone 8. It can be damaged by freezing temps, and the damage increases as it gets colder. This article has more information: https://www.gardeningknowhow.com/ornamental/flowers/bop/mexican-red-bird-of-paradise.htm

Here's an article that should be of help to you: https://www.ctahr.hawaii.edu/oc/freepubs/pdf/OF-27.pdf

I had never heard that, and in my (rather short) research, I couldn't find any mention of it. A couple people thought bird of paradise hard to compost because it doesn't break down easily, or tends to take root instead of composting. However, I didn't see any mention of the plant as alleopathic (https://www.gardeningknowhow.com/garden-how-to/info/allelopathic-plants.htm
Also, if a compost heap is working properly, the plants will neither root nor fail to decompose:
https://www.gardeningknowhow.com/composting/basics/ultimate-beginners-guide-composting.htm