As others have noted, tire pressures are easily calculated based on tire width and bike+rider weight and there are multiple calculators available for making that calculation. I use the Rene Herse calculator myself because the science behind it is thoroughly explained and well thought out.

I've never lowered the tire pressures for storage (they do that all by themselves) and I've never noticed any difference in post-storage ride quality depending on whether a bike is suspended or not. Note that there's only about 10 to 15 lbs resting on each wheel when you're not on it so that seems like a pretty insignificant load. I wouldn't worry about it. That said, it is probably detrimental to store a bike with completely flat tires on the ground because they may take a set that is a less than ideal shape and may crack where they are folded under.