Big post!
I am all PC, so am probably limited in what I can add, but I notice a few things.
First, system latency? If this is set to very low, you will get instability. Better in general to work with greater latency where possible. I make mine low when playing in fast keyboard parts and Constrain Delay isn’t enough. But set latency high when mixing for better stability.
Audio set to boost?..I’d say not necessary as any half-decent computer will stream masses of audio on the standard setting - your system should be easily fast enough.
SSD? You could put libraries onto a super fast drive. But that shouldn’t be necessary. I have my systems set up with three regular active drives and a daily offline back up. That is: System / Audio / Data libraries and Backup. Nothing is bottlenecking
Also, I do limit memory a bit on hungry VSts such as BFD - I run 16 bit rather than 24
Some DAW users fall into the bad habit of assigning fresh reverbs etc to each channel as inserts…if that’s something you do, it will eat massively into your headroom. Better to configure reverbs as send effects
Same with instances of VSTs. If you have a multi ouput intrument, open one instance into the rack (F11) and assign MIDI channels. That’s way more efficient than loads of Instrument channels.
Finally, is your system - especially CPU running hot? If so, that will slow you down as most modern systems throttle down to protect CPUs. Last Winter, for example I purchased a ready made PC…it worked well until Spring and then seemed to get very noisy and very slow. I eventually realised that the CPU / fan vent arrangment was terribly badly thought out. I ducted in fresh air properly and that system goes like a bat out of hell now.
Sorry if these comments don’t apply or help, other people will no doubt chime in with useful ideas.
Best of luck
P