Hi Doug. Congratulations on your new tank.
The polystyrene needs to be about 2.5cm (that is what is under my tanks anyway)
Depending on what the tank is going on, plywood may or may not be overkill.
Putting stuff in the tank is not going to affect the glass, unless you drop a rock on it
Good plants would be Java fern, moss and Anubias. Hygrophila is a fast grower too.
Nothing wrong with the fish mix but tiger barbs tend to be nippy.