cool, looks good. And I hear ya….a lot of money for foam!
So are you going to fill the the rest of the shower area with 3/4″ sub flooring to get even with the rest of the subfloor?
And definitely use the subliner over the strata mat and pan.
Its nice to buy enough to overlap each portion 6″ or so
I really don’t think you will need the backer board in the rest of the bathroom. By the time you thinset that down…you will be at least 5/16″. making the overall height in bath that much higher than your 3/4″ outside flooring