You can see where on the picture your dust spots are, so compare that to where in the lens you saw dust. Does it correspond?

No. Without a lens on, the picture is completely unfocused, so any dust spot will be “spread out” over the entire picture and not be visible.

Yes. I don’t know exactly why, but I’ve been shooting digitally for 15 years and have dealt with sensor dust a lot.
I’d first clean the sensor with a swab and cleaning fluid, then test again before you do anything to the lens.

Opening up the aperture will make dust on the sensor much less noticeable, too.