In Direct3D period, and indeed row-major matrices period.
In a left handed system
Why is there suddenly all this confusion about handedness?
The difference between left-handed and right-handed doesn’t exist until you render something to the screen, in which case the projection matrix is different. Until then, nothing else changes.
Just a note, sin() and cos() are more than expensive. Never call sin() and cos() with the same values repeatedly. Store them to locals and use the locals.
Here's my code of composing a model matrix: