Indeed. With enough energy we can convert recycled plastic into literally anything. All you need is to fuse the right nuclei together.

It might need more energy than you would spend mining it from a distant star system, or release enough heat to melt the factory, the crew, and the planet it's on, but, still, there is no fundamental law of physics preventing you from doing it.

Yes. Basically for this to be economical, it would have to be both low cost and more high in value than alternative ways to recycle plastic. Basically making plastic out of plastic probably takes less energy and results in a more valuable product that can be recycled more than once. Alternatively, burning it and using the resulting heat for energy generation is also very common.

And then there is the question of scale and sustainability. Recovering hydrogen from what is essentially a product made from fossil fuels to then burn it is not really that helpful. And there is only so much plastic out there that we can recover. At best we get a second use out of the fossil carbon before it is released back into the atmosphere. But you could argue that a landfill at least captures the carbon more permanently. So, labeling this as green or sustainable would be a bit of a stretch of the definition.

Yes, whilst including full operational costs (e.g., dealing with waste).

There was a recent posting here about a company in this space using pyrolysis to break down the inputs but had serious issues in emissions from the plant.