Welcome!!! I would say, like has been said, just add salt and go. The design of your overflow will have noise. some advice on alternatives has been given and are solid options. The setup you have looks ready. My only advice would be to forego the "biological chamber" and use that area for a skimmer and add coral rubble around your skimmer for extra biofiltration. Additionally, and this is just one opinion, I would skip the two-stage drain section and opt for micron filter socks instead. You'll be in there a lot taking out and cleaning/replacing the fine mesh often and digging past the course section, dislodging particulate will become tiresome. Just pull socks and replace them with clean ones and go on cleaning the dirty ones as needed. I have about a dozen socks that I just rotate.
Can't wait to see some life in there!