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I like to use sharp, clean pruning shears, or those kitchen scissors. Both will work fine. If neither of these are available you can use a sharp clean knife. You can dead-head, and cut off any dying leaves.

Here is an article for proper pruning methods: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-pruning.htm

Wow! Whatever you did worked. Usually the blooms will last no more than about a week before they start to die off. Here is an article that will give you more information on growing these: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-blooms.htm

This can happen sometimes, and is no reason for concern. This means that your plant is happy and healthy. Here is an article for more information on the plant: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-an-exotic-flower-like-none-other.htm

There are some pretty strict conditions that must be met in order for the seeds to germinate. This article will explain the process: https://www.gardeningknowhow.com/ornamental/flowers/bop/propagating-birds-of-paradise.htm

This appears to be normal markings on the leaf. If you see this spreading along the tips, or the edges of the leaves, then this would be a cause for concern. What you are seeing here is completely normal.

Here is an article to refresh you on the care of these: https://www.gardeningknowhow.com/ornamental/flowers/bop/

Birds of paradise most commonly turn brown if they have been affected by frost or exposed to a drought. If your area has experienced freezing temperatures lately, this is probably the cause. It's best to wait until spring (when there is no chance of frost and when plants start to grow again) before pruning, which will help the plant avoid any further damage. Then, you can remove the damaged parts or cut the entire plant down if it all seems to be dead. It may still come back from the roots.
https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-paradise-plant-freeze.htm