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If the leaves turn black and curl up, the plant is probably being kept too cold. Make sure it isn't too close to a window. It prefers warm temps like between 65 and 75 degrees.
If the leaves stay green but curl up, that is a sign of too little light. Try and keep the plant within 5 feet of a window that provides at least 4 hours of direct sunlight a day for best results.

We cannot recommend specific places for purchase. I would check your local nurseries, or online.

I would use clean, sharp pruning shears for the job. You can prune off about 1/3 of the plant a year. Anymore than that and you risk killing the plant. This article should help: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-pruning.htm

I am sorry to hear about your plant. This year's weather has been hard on plants. Wait until spring and only prune back leaves that are brown. Leave anything green intact.

A slow release fertilizer like Osmocote works well for them. This gives them an even amount of fertilizer in between feedings.

The easiest way to propagate these plants is through division. This article should help you with that: https://www.gardeningknowhow.com/ornamental/flowers/bop/dividing-bird-of-paradise.htm