When using extension tubes the lens focus ring only changes the focus about a foot for the shortest tube to a few inches for the longest tube. Focusing is accomplished by varying the distance to the subject. The shorter the lens focal length the closer you have to be to the subject. Extreme wide angle lens won't work as the point of focus occurs behind the lens and its impossible to put the subject there. I use a 35-135 zoom on a F4 with a 20mm tube and a zoom setting of 40mm to 70mm depending on subject. Bees don't like you too close to them.
No, I haven't been stung but they move away.
Depth of field also decreases significantly even at small apertures.