1.a. How far is it from the Earth to the moon?
1.b. How far is the Earth from the moon?
1.a. and 1.b. are pretty close to being identical. In practice, 1.a. would be more likely to be used if someone were planning to move something from the Earth to the Moon, or if someone were planning to travel from the Earth to the Moon.
For example "That astronaut is going to travel to the Moon." "Oh really? How far is it from the Earth to the Moon?"
"The Moon looks really small even thought it's not that close." "Oh really? How from is the Moon from the Earth?"
But I say the usages are "more likely" because in reality you could hear either sentence in either situation.