If somebody ever made a card with Crew 0, would the following be true?

1) You have to tap something to turn the vehicle into a creature, but
2) That something could be a Wall or something else with power 0

Both would be true.

I disagree. The cost would be "Tap any number of untapped creatures you control with total power 0 or greater." 0 is a valid choice for "any number" and the total power of a group of 0 creatures is 0.

So I think you could activate a "crew 0" ability without tapping anything.

I don't think you could get away with crewing a vehicle by tapping no creatures. I mean, 0 is still a number right? You would still need to tap something to fulfill "0 or more power."

I agree with CommanderJim's assessment. "Nothing" is always a valid choice for "any number of [something]", provided the other conditions are met, and the total power of nothing is 0.

I would argue (perhaps incorrectly) that the total power of nothing is nothing, which is different from the actual number 0.

"107.2. If anything needs to use a number that can’t be determined, either as a result or in a calculation, it uses 0 instead."

If you sacrifice a Sword of the Ages with 0 creatures, it deals 0 damage to the target.

I don't think we even need that rule. The value of an empty sum is zero.

By convention the empty sum is 0, no reason for Magic to necessarily hold to that convention.

but if it broke from mathematical convention, one would assume it would tell us somewhere.

well, sure, but evermind's converted mana cost is still 0, not N/A.

If they ever printed a Crew 0 card, I'm sure they would update the rules such that Crew N meant "Tap one or more untapped creatures you control with total power N or greater: This Vehicle becomes an artifact creature until end of turn." I mean, they changed lifelink and deathtouch (both of which started their keyword lives as triggered abilities) so they would work the way they intended for them to work. And I'm pretty sure they intend at least one creature to be tapped for Crew abilities. But as currently worded? I agree you could technically declare an activation of Crew 0 without tapping any creatures.

I have a feeling I'll understand why this topic exists when I check YMtC.

Lemme be honest: part of this discussion was meant to determine the viability of of designing a card with Crew 0. It appears said card is not viable.