If putting your pots into the background then you wouldn't need to have holes in the bottom since there usually wouldn't be drainage through the background. I usually silicone branches and wood accents into place then GS foam around them to keep them in place.
You can also make a hole in the GS foam later to slide branches and vines into and silicone them in.


Remember to design in access to your pump for the waterfall in case you have to service it.