I just published a PyQt5 book:
Even Phil Thompson, the creator of PyQt, read it and says it's "very good". It saves you a lot of time when learning PyQt. It's the resource I wish I had had when I was getting started.
I also wanted to install just Qt Designer. Like you, I found it very difficult, without having to install gigabytes of other software. Out of this frustration, I created standalone installers for Qt Designer for Windows and Mac. Maybe you will find them useful.
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