Simple RAW for 5e V: The Disadvantage Strikes Back

[Millstone85]

Q3 Is it correct that only attack rolls automatically succeed on a natural 20* and automatically fail on a natural 1?

Yes, this is correct.

*and are critical hits obviously but that wouldn't apply to other checks anyway

Highlighting mine. Note that attack rolls are not ability checks.

For example, when the hex spell imposes disadvantage on ability checks, this does not apply to attack rolls.