.i agree with the others. Build up the hull and deck Paint both in their final colour THEN install the wooden deck.
As for PE railings (or any PE for that matter)I work from the centre line out. This minimizes the risk of knocking PE off..
So ion this basis the main deck railings are generally the last pieces to be installed
Good luck. pe is like a great partner. You love it , looks lovely, but sometimes it drives you crazy
Barry