I recently refloored and restepped my outdoor deck with 5/4 kiln-dried quartersawn white oak, random widths. About 500 bd ft were delivered. I asked the driver who delivered it how much it weighed. He said just over two tons. That's about the same as a cord of dry white oak weighs.
That was a whale of a project, but that deck is now solid as a rock. Ipe would have cost about the same, but I went with the domestic stock. White oak is tough stuff.
The 14 stair treads are 51" wide. The deck is about 15' x 24'. I wrote a computer program to allocate and shuffle the random-width boards on each half. Here you go:
I'll use Flood CWF. That seems to be as good as any. No need to add stain to it or anything else. One coat every two years or so should do it. Of the oaks, white oak supposedly has about the best natural weather resistance, similar to Ipe.
There is no error is your math, but your waste assumptions are improper. You lose about 65 to 68% of the log when you convert cordwood to board feet of sawn lumber. Hard to believe but true. The waste factor is rather large, especially if the log is quartersawn. Plainsawn provides less waste, so quartersawn and riftsawn hardwood is more expensive. Woodworkers often pay the extra amount because plainsawn will usuallly have more crook and bow.
