In regard to installing 5/4 (1x6) treated wood decking. Do I need to install it with the growth rings facing a certain way, to help stop twist and cupping?
Yes, that will make your deck look more uniform.
install them with rings looking like they're an upside down bowl. then screw the deckboards to the joists, 2 screws per joist about 1" in from the edge of the decking board.
If you are buying dedicated 5/4 decking lumber, the point is mute since the back side will normally have several small groves cut into it along the length of the board. This is to aid in controlling cupping or bowing of the board.
If you take a close look at the lumber the growth rings could be on the edge.......