If I am planning on buying a product such as the one shown here and to support it using a solution such as the braces shown here - How often would you place a brace - Is every stud (~16") overkill, can I get away with every other stud (~32"), further? - I don't want the desk to flex under any foreseeable circumstance. (dumb teenager deciding to sit/stand on it for instance). I can't find any recommendations for a support schedule.
The site you linked states "space the brackets 18 - 24 inches apart" source 1 source 2, with the first 4-6" away from the edge. Because you definitely don't want it to flex, even under abuse, I'd err on the side of caution.
With a 8' desk:
- 24" apart would be 4 brackets.
- 18" apart would be 5 brackets.
- 16" apart would also be 5 brackets.