The need for constant expansion is one of the most damaging aspects of capitalism and is one of the main issues that ParEcon seeks to address.
All of your questions and more are answered here:
http://www.zcommunications.org/zparecon/parecon.htm
I found the theory far more substantial and well developed than the theories that promote and support capitalism, which are usually less than insightful and are more along the lines of rationalization after the fact than viable working theory.