I still think that even in your deeply nested example, each bar and wizard would have their own URI which wasn't nested.
Q1: singular or plural doesn't matter but be consistent. I find plurals work well grammatically.
Q2: /images/452 for the individual image, probably /users/123/images for all the images for that particular user.
Q3: yes :) I often use a basic MVC approach, such as in the open source joind.in API, which you can find the code for here: https://github.com/joindin/joind.in/tree/master/src/api-v2