Any suggestions for the best way to visualize the data once we have it? Are there some existing LIMN graphs that would be well-suited for a funnel analysis like this one? Or should we simply use a standard line graph as we do for other descriptive metrics studies?

Limn doesn't have many graph types but it might have a decent one for this purpose: http://debugging.wmflabs.org/graphs/ordinal_example

So you could have Step 1, Step 2, Step 3, ... on your X axis, then the number of people who made it through each step on your Y axis.

For a better funnel visualization, we should really support Sankey diagrams: http://www.practicalecommerce.com/files/images/0005/0938/2_goalFlow_Large.png