I've used pressure treated and non. The regular lumber lasts years also. I'll probably move and have to tear down some buildings before they rot.
The concrete deck blocks work very well. You don't have to dig holes and they keep the lumber dry. With them, all you have to do is paint the bottom...
It depends on what it is treated with. Newer treatments are less hazardous. The wood should either be stamped with the chemical or the supplier should be able to tell you what it is. You certainly don't want wood treated with inorganic arsenic.
Look for products certified as an Environmentally...