I well understand the changes as you move forward. If possible I normally start with a SketchUp model and then print various views. From the printings, I start the build and write-up. During the build, I will make necessary changes to the actual build as well as the write-up and SketchUp model. After I complete the build I then let things sit for a day or so. Then I return to the project to review my model and write-up. Almost always I will make more changes.
What source did you find for the bearings/wheels? I'm not sure what to search for. I'm leaning toward more of the jig to be made from metal. My son is a welder and can help me. He also has a close friend that has a metal lathe that can be used if necessary.