That is totally up to the shooter. Also, you can use a smaller aperture and get a bigger DOF so you don't have to worry about thing being out of focus.

Some other use told me that you can't fix ISO or shutter, so f8 may not be an option.
I don't know, just noticed that all videos here struggle with focus.

Welcome to the world of motion pictures vs stills! On a film set, there is a job position called "focus puller". They have a special attachment on the lens to control it (even remote controlled nowadays). They block out the scene, set markers on the ground and measure the distance to each one. As the actors hit the marks, the focus puller adjusts the focus to the pre-determined setting by distance. The camera operator doesn't even touch the focus. So if you want that DOF along with a moving subject in focus, that's pretty much how it's done. Nothing to do with the camera's limitations.