All of the above, plus the price of that size of pvc is much more than the lumber needed to make a stand. I would even trade foot for foot, that pvc pipe for 2x6 lumber if you were local.
The most critical is #3, pvc is designed for holding internal pressure, it does have an incredible burst strength for its weight. It isn't very good under compression.
If you are near Chicago let me know, i'll get the lumber for a trade.