You could create custom columns in a report to satisfy your visual needs. You won't really have percentages, but you'll be able to see the total leads, then a custom column for each response with however many leads responded with that answer.
You'd just need to create smart lists with the proper filters for each response and add those to the setup of your report.
Regarding your alternative method, you could accomplish that with jQuery, except I don't know how you would submit the form. If you had control over the confirmation page for the Google form and were able to pass the results through to that page, you could execute the second form there, but I don't think you'll be able to do that with the Google setup.
I'd give the Marketo way a try and see if that is enough for you.