I dont know how you typically troubleshoot systems or your experience, but when I have a problem like this I always tear the system down to its bare necessities and add in a part at a time until it breaks. If it doesnt get better then I start swapping parts based on what I believe to be wrong.
Given that it seems to be freezing up during boot that would be my first steps.
I’m not trying to brag but I’ve worked in computer repair shops, I have my A+ cert (not that its worth much), and I’ve been building for well over a decade now. People usually bring things to me to fix. I’m far from the smartest person on this forum but I did learn from a few smart people over time. That method has always been my go to and it seems to work more often than not. Sometimes its a broken part, sometimes its a simple mistake, sometimes I dont find anything wrong and putting the system back together leaves it in a working state and I’m left scratching my head. Almost always I fix the problem or find whats wrong.
Spare parts are always nice to have on hand if you can try known good stuff too but I know you probably dont have anything you can really swap on this system.