It will work on multiple items at once - I don't know about Iron Chests, but in my 'Resource area', I'm running 11 different metals through a regular wooden chest and haven't run out of slots yet. SP2 is a Solar Panel level 2. If you don't have a spare lying around, they're pretty cheap to build.
The duct on the back re-cycles the product through the system (so your product can be compressed to the next level). That setup in the picture is for compressing cobble. Compressed Cobble gets shipped back to turn into Double Compressed and so forth. The high-grade servo is for speed. For metals, you'd want a pipe with a servo to pull blocks out of the system from the second chest (with 11 metals, a Signalum Servo will do comfortably).
The duct on the back re-cycles the product through the system (so your product can be compressed to the next level). That setup in the picture is for compressing cobble. Compressed Cobble gets shipped back to turn into Double Compressed and so forth. The high-grade servo is for speed. For metals, you'd want a pipe with a servo to pull blocks out of the system from the second chest (with 11 metals, a Signalum Servo will do comfortably).