I know you asked PK and no me, but I suggest getting FireAlpaca. It's a new free program that is suppose to be like SAI and it has a version for Mac. Then you could follow PK's SAI tutorials.
i do have it, but it's REALLY simple and it doesn't have much at all. i haven't used it in a while, but i think there's only one brush too, and you can't change blend or whatever like SAI does.
there is more than one brush and the blending goes smoothly in my opinion, but the program choice is up to the user so please do your best in whatever program you choose.
how do you suggest painting in PS?