Teaching quantum computing to a (really smart) toddler
medium.com
medium.com
I know a bit about quantum computing too so I did a high-level fact checking of your post without finding any bugs. Impressed you managed to do math equations on medium. It is a bit long though... saved to continue later.
On a different note and for a different perspective, you should check out this excellent review paper by Sara Robinson, Emerging Insights on Limitations of Quantum Computing Shape Quest for Fast Algorithms: https://www.siam.org/pdf/news/100.pdf It's an old article, but all the points she raises are still valid. I think it's going to be REALLY hard to get large number of coherent qubits to do computations.
The detailed challenges of extending coherence time are mostly hidden to those whose primarily research tools are search engines and textbooks such as myself. This is the realm of proprietary tech, all I can do is speculate based on the credibility of those making large investments in the space that those in the know see potential.