I think you may run into problems....
For the line of code with the error you can just remove it and make sure to remove the closing "}" below that corresponds to this line of code. It isn't necessary in your case.
The problem I am anticipating is that paypal probably won't allow you to pass free items using the paypal standard system. Your technique would work in that everything would look correct on your site, but checking out will be a different story.
You may want to leave it as is and remove the itemized cart information. Pass all the cart information with FullDetails and use the charge as the amount field. Basically I'm recommending redoing the hidden form elements using the paypal standard documentation instead of using the standard format the wizard creates becuase of the unique differences in your cart.