You can mix and match USB2/3 device without worrying about speed drops, but I normally connect USB3 to the USB ports supplied by the motherboard chipset and USB2 to any third party chip as these are not as efficient.
PCIE-3 lanes run independently.
SATA device run independently.
Perfect. Much thanks. I had a simple question, but Googling kept telling me only about backwards compatibility that I already knew.