How do I make a symbol that has my desired dimensions without stretching the text? 

Read the guide to resizing symbols.

Does the project intend to support 2D barcodes?

Yes, in time. Follow this thread for a more thorough explaination: 

http://groups.google.co.uk/group/postscriptbarcode/browse_frm/thread/cfbbee01e20d89ac/9c2c45aa6d5424a4?#9c2c45aa6d5424a4