The worm's description implies baseline Low 2-C whereas Alduin can outright kill 22 Low 2-C beings in a single attack, so he has the advantage in AP and Durability. However, The Worm can passively mindhax Alduin. My vote is inconclusive.
Alduin could kill an abstract like the worm. As noted in the profile, Alduin "Can rip time asunder and devour all of time. Can slow and stop time in its track, or accelerate it. Can devour an enemy's time, making them grow younger or older" and "Everything that he eats is erased from time itself". This would mean he could directly affect time and destroy the worm if it weren't for the passive mindhax.
Nope, mindhax can't fuck with Alduin. Not to mention, Alduin has void manipulation that he can affect the non-existent beings as well. The Worm won't escape the stomach of World Eater, which I woud vouch for that
I don't see how it is relevant. Alduin has affected abstract beings like Shor and Leaper Demon King (Dagon) slightly above the Worm here with the exception of Shor. He traded blows and defeated one of them removing the abstract concept and imposing another on LDK.