I ride at 50-65PSI. I like to reduce rolling resistance and this seems to be the best way to do it, given the weights I have to deal with. I'd do higher PSI but I have only ever had one tire that was rated higher, and it's too wide to use on either of my current bikes without modification.
TIre size varies depending on which bike and which stage of experimentation, but I usually use 26" wheels. 24" on CrazyBike2 originally (it is now 26" until I get a 24" motor wheel built). The unfinished ReCycle would've used 26" rear and 20" front. The new bike in progress will use a motorcycle wheel and tire, it's probably 3-4" wide and just about 26-27" outer diameter; I don't remember what PSI it uses. I'd prefer a skinnier tire/wheel but I don't have anything else that's anywhere near this strong for cargo carrying. Moped wheels would work, I think.
Width/size varies depending on what tires I happen to have salvaged, because some are up to 2.5", most are 1.95" to 2.1", and some are closer to 1.5" skinny tires.
I prefer softer tires with stickier rubber, and smoother tread patterns. I have only ever found one pair of tires that is ideal, and they are now both totally worn out, with holes in them. Everything else is a compromise, either too slick or too knobby. Softer tires give more even when at higher pressure so they ride smoother than hard tires. They also grip pavement better, so less chance of me sliding out in a sudden sharp turn (like avoiding a car or pedestrian making a sudden unpredictable maneuver into my path). But they wear out a lot faster than harder tires.
