I've used two of the nylon Petzl "emergency" pully and two tiblocs for doing short glacier crossings as a "just in case" set up. You can set these Z systems up with prussiks and ovals but it's not pretty. The nylon emergency pulley is the same thing used in the Sideswing Pulley but when you're using the nylon on an oval, if the pulley breaks you still have the oval holding your rope.
It depends on what your trying to accomplish and where you're trying to accomplish it as to what you might want to carry and have as well as how you want to set it up. What are you trying to accomplish?You're going to expirience alot of friction at your #1 and #3 points. If this is a "just in case" system I would say to go with the lighter nylon pulleys, you can carry 10 for the weight of a regular pulley. If you're going to be doing alot of heavy hauling get some nicer pulleys and get atleast two.