Not sure WHERE you have studied it all. A good source of reference would be helpful. Islamic Golden age is a time of no return. Western nations and their East Asian allies have gone at least 1000 years ahead of collective Muslim world already
Multiple places, some seminars, lectures, books etc and I haven't studied it all, but the basics. One can never learn
all of something as complicated as this. I'm pretty sure you can study most of what I have through the internet alone.
I gave a few links in my previous posts, and they have references to Hadiths and books by historians, have a look if you're interested
Yes, the Western nations have gone ahead but I wouldn't say 1000 years since it's only been about three hundred years since the West gained political superiority over the Muslims, but it's significant enough. Every empire has its sun set, eventually.
These were various forms of monarchies, sultanates, war-kingdoms all titled as Caliphates. Real caliphate, the rightly guided one ended after Ali's assassination
Many, if not most of the following Caliphates, like the Ummayads and the Abbasids, kept most Islamic rules and were pretty close to the rightly guided ones, though admittedly they had plenty of flaws.
I agree with pretty much the rest of what you've said, yes, Ijtihad has been politicized (not shut down, per se, but made pretty much dysfunctional unfortunately) and it is no longer practical to apply Islamic law the way it was done a thousand years ago.