The dowels are poplar or pine. They are .5" diameter. It's a very snug fit with the 3D printed models. It works very well. I was working on a parametric design for these with openSCAD. Basically you would enter in the dowel diameter, the number of connections, and the angle between the connections into the program. Then openSCAD would generate that model. Which could be imported into a traditional 3D program, Blender in my case, and used to build something. If you are interested in the parametric design I would gladly put it together and post it.
I used to have carpet pads to reduce vibration. I removed them because they are not very necessary and they were ugly.
This table does wobble a little bit. I am thinking about building a shelf on the bottom for my wrench toolbox. Which weighs a good 40 LBs. That would help to keep it from wobbling while the printer is going. The table is not wonky, it wobbles because of the carpeted floor.