Given time to reflect on what I said above, if you are going to use plywood for the cabin sides I would not even bother with the aluminum. I normaly use balsa for my fuselages and try to keep the use of metal or plywood to a minimum. In your case I would just fiberglass both sides of the ply with lightweight cloth/epoxy and leave it at that. Now as far as the rods 1/4 inch hardwood dowels should suffice. That is how the wings on my Belanca Airbus (flying W) mount, and it has a 120 inch wing and is pulled by a zenoa 35 cc gas engine this plane weigs in a 20 lbs.. Now I fly it scale and do not use it for aerobatics much but have had no problem with the structure thus far. Laminating a thin ply to the root rib might be a good idea to secure the sockets better but might be overkill.
The main goal we have to keep in mind is to keep the airframe as light as possible, that will give you the best performance. I have found it all to easy to over engineer my airframes in the past adding lots of weight in the process.