Hard fork and low tire pressure or viceversa?
I don't think tire pressure should be set on how cushy you want your ride (unless you have no shocks).

Tire pressure pressure and tread selection should be done based on how much traction you need. The trade off is that with more traction, you get a higher rolling resistance and you need to exert more energy to cover the same ground. This is why road bike tires look different than mountain bike tires.


More traction => Lower tire pressure, knobbier tiers.
Less traction => Higher tire pressure, smoother tires.


After you figure out what tread and tire pressure is best for you and your riding enviorment, then you can think about dialing in your fork and stiffness and damping.

Fork stiffness is somewhat subjective, but it's probably best to set it so that you only bottom out the shock when you take a pretty big hit. Most people set the stiffness of the fork based on sag, sag is the percentage that your shock deflects under your static body weight. Most people set their shocks to sag between 25-33%.

The fork damping (what you call rebound) should be set so that for your weight the fork is critically damped. No if's and's or but's about this one, physics dictates that the best ride is one where you are neither under or over damped.