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#51
As far as the amount of space, that is up to you. I normally allow 10%. but it depends on the free space on your SSD. When we do a clean install, F will not be in the picture and you can have C on and F off.
If you are planning a clean install soon, AHCI can be configured then. Anything you do now, will be undone then and really won't matter. I would strongly advise a Clean install soon, then wipe F clean and start over. That will resolve any of these problems. I can't say this is what is causing your problems, but I can say it certainly does not help in the operation, performance and discovery of what the problems are.