The vertical load capacity of a "plain" wooden post will depend on its height. You can load a 6" x 6" post that is up to about 10 feet tall that is sitting under a spreader beam and on a sill to something like 15,000 pounds. But this is exclusive of any torsional or deflecting loads, and you know why. A beam loaded to capacity in the vertical that is then subject to any significant lateral or torsional loads will almost certainly fail. Structural engineers earn their living making calculations like this in various situations. And they are worth every penny.
Hundreds of pounds
A 6x6x8 cedar post typically weighs around 80-100 pounds, depending on the density of the wood and any moisture content. The weight can vary slightly based on the specific characteristics of the wood and how it was treated or processed.
No
36
6x6=36
36
6x6=36
That would depend on how big the addition was.
I use one bag to 1 1/2 bags per hole and fill the rest of the way back with tamped topsoil... whatever came out of the hole.
6x6 = 36
6x6 in standard form = 36
It depends on the type of beam, the material, whether it is a bridge span or cantilever, the allowable deflection and safety margin needed. We need a lot more data on the application.