MicrostockGroup

Hehe that's a weird question!
It doesn't matter, as long if your photo is sharp and noiseless. And every image needs another DOF, depends on the subject!
What ISO setting is best for microstock would be a better question; so low as possible.

Yes. The author of that webpage used a few too many Google ads, though.

Yes, a very high F stop intoduces a phenomenon called diffraction which causes deterioration of sharpness.

My Nikkor 35mm F2 for instance starts to deteriorate at about F14 and I can see an obvious difference in sharpness if I take the same shot at F11 and F16.  Consequently I never use this lens at more than F13.  Between F2.8 and F13 it's wonderful.

Macro lenses tend to be optimised for deep DOF so my Nikkor 60mm Micro takes perfectly sharp pictures all the way to F32 and is best between F11 and F32.

Check the MTF graph of the lens and try to shoot within the sweet spot for your lens.

A f/2.8 lens does not mean that it will be best at f/2.8. Sweet spots are usually between f/5.6 to f/11.

Very valid points.
But to come back to the initial question; I don't think there is a wrong F-stop for microstock.
I've had F32 images accepted on IS,SS,StockXpert and DT, made with my cheap ass kit-lens, on-camera sharpening off, and no additional post processive sharpening applied.