Also, we made auto-load stations out of 1/2" square hardwood stock, purchased in Home Depot in the millwork/moldings area. With 1/8" hardboard bases which could be weighted for rough play. I don't have the dimensions handy other than to say it's exactly 1/3 scale. Again, assembly was gorilla glue and #6 screws.
Cost per auto-loader was about $5.00 per station.
Here's almost 1/3 of a 1/3 scale Triple Play field at the New England FIRST conference.
This whole setup is a real show stopper anywhere it went.
Don't worry about weight of the tetras. The Vex Gus was able to lift three one pound tetras at once. It had a two stage arm gear box (I think it was two 4:1 stages) and the elevator used a 4:1 gearbox to a 24 tooth sprocket. The two stage elevator used only single chain to lift and worked very reliably. We've had maybe 15 or 20 chain separations or breaks in two years. Changing the lift mechanism to double chains would probably make it nearly indestructible.
(Actually, this picture shows Mini Gus with the version 1.0 elevator made out of starter kit parts which still worked very well.)