It is suggested to apply through both ways. If not, then applying through portal is the must, and sending application materials to hiring faculty is highly recommended, you can find the hiring faculty’s mailbox under “How to apply” section in the Job Description.
Yes, you are encouraged to submit reference letters as attachment when you apply, or you can also provide the letters later during the reference collection stage.
You may consult with the hiring faculty about specific request on the recommendation letters.