9x3 is way too heavy, that would do a single span, you could use 4x2 if supported every 2 or 3 feet or 6x2 every 3 or 4 feet,
I used 8x2 because it was as cheap as 6x2 at the time, get the support foundations right and the rest is easy, I like the idea of the tube pillars as it would be really easy to level your foundations, just watch the height compared to the width. The higher the pillar the wider the tube
Chickadee's