with the cooling time, you won't be able to do 20 and also my question is not about how many batch an hour but how many batch can this machine handle per day or week.
Also, Sonofresco would be good idea for the show( i did think about this) What good is it broken roaster on your show room. Also sonofresco gets pretty dirty around glasses and that also discourage me to purchase it few years ago.
It would be better to put used drum roaster as display then brand new sonofresco.
I found that as long as you give it a wipe with a dry cloth after each roast it stays clean. I just spray some water on a J cloth and give it a wipe. I think it would only be an issue if I were to roast practically to charcoal for an entire day without cleaning it at all. I can dump, clean and reload comfortably in about 1 min.