1: i got a zoom lens full of white shining dust inside the lens element, i never found it affect PQ. dust normally doesnt affect PQ unless is very large amount like u hard to see through the lens by ur eyes. or haze will reducce the contrast of lens. dust spot wont appear on picture
2: forget about it
3: not sure but i think is not.
PS: even a cracked glass wont show in ur photo, but it will reduce contrast and sharpness.
so u can imagine how much of dust will only affect PQ like a crack lens.
hope these sample will let u feel better cheers
