Learn English – the meaning & tense/verb phrase of: ‘I had been away for almost five years’

The phrases all mean the same thing but (1) is the most common in both cases I think, although in most informal usages "I have" would be shortened to "I've".

"I never met you before" is probably quite common before as it is shorter and the meaning is clear.

"I had never been here until now" would be strike most native English speakers as strange way to phrase it, although they would understand your meaning.

The perfect tenses (past or present) imply some completed action occurred before some other event and has some relevance to it.

"to go" in general implies motion or a process; thus in the perfect tenses it implies a completed action with continuing relevance. The continuing relevance can in some cases imply the subject has not returned

But not always:

I have gone to England every summer for the past ten years

The modifiers "every summer" and "for the past ten years" rule out the possibility that the subject has not returned (you can't go somewhere you already are).

I tried to change "gone" to "been" in all these sentences and it just doesn't seem right.

Been to actually works in those sentences but gone to seems more natural. Using "been" also seems to shift the meaning slightly in someways.

"had gone to law school" for instance seems to imply completion more than "had been to law school" would.

Is this use really common?

I think your concept of contrasting gone to with been to is too strict. Yes, been to implies somewhere you are no longer (because perfects represent a completed action), but gone to doesn't always mean you are no longer there. It can depending on the context.