What's your question? Ask

I would recommend trying a different spray. I like to use neem oil as it is absorbed by the plant itself and kills any pests that bite the plant. This means that coverage is complete and will not be washed away if it rains.

It could be a few things. A lack of humidity may be making the blooms dry out prematurely. This would result in dry, brown blooms. You could have a fungus called rust. This would create a powdery, orangish dust on the blossoms and possibly the leaves. You may also have thrips. These attack the base of the flower and are hard to see, but would also make the blossoms fade to dry and brown.

If you suspect humidity, mist the plant or set some water near it to evaporate and raise the humidity. If you suspect rust fungus, treat the plant with a fungicide. If you suspect thrips, use a pesticide.

You can normally cut them back by a third without harming them. This article will help you: https://www.gardeningknowhow.com/ornamental/flowers/camellia/pruning-camellias-how-to-prune-a-camellia-plant.htm

This is sooty mold. It is a byproduct of a pest infestation, likely aphids or scale. This article will help you with getting rid of it:
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm

Neem oil can also be effective. It will take care of both the pests responsible as well as the fungus. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

You can do that. Don't remove more than 1/3 of the plant in any one year, but beyond that, you can reshape the plant as you wish. This article will help:
https://www.gardeningknowhow.com/ornamental/flowers/camellia/pruning-camellias-how-to-prune-a-camellia-plant.htm

These articles will help you with transplanting itself:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm
https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm

It may be helful to repot the plant while laying it down. This generally makes it easier to handle and the plant is less likely to be damaged during repotting. Use a long knife to run around the inside of the pot and loosen the roots from the pot.