I think that if you stick with the game you will eventually want an absolute minimum of 10k/12h production. Cephalad's idea of clusters isn't for me. He uses 1 field to support each 6 farms. In this setup I have double that. This is using normal Silos. If I got some improved ones then I could swap out 12 Silos for 6 new ones plus 6 more farms. So I would have 20 farms sharing one field. The space saved compared with Celephad's approach more than makes up for the slightly lower production.

I would advise that you don't worry about working out the theoretical balance too much - just monitor how the field depletes. In my set up some farms and silos have further to walk so are less efficient. If I were doing it again I would place the silos in the best positions and make the farmers walk further. This is because silos are more expensive to buy and upgrade and to offset the issue that Fexno described.