Voracious Wurm and Wall of Reverence: which trigger happens first?
No.  Replacement effects do not use the stack; as rule 614.1 (which you quoted) says, "[R]eplacement effects apply continuously as events happen" — i.e., they happen immediately, at the same time as the event being replaced/modified (in this case, Voracious Wurm entering the battlefield).  Thus, if Voracious Wurm enters the battlefield before the beginning of the end step, it won't benefit from Wall of Reverence's lifegain (but the Wall will be able to target the Wurm later).

However, if the Wurm somehow (say, by giving it flash) enters the battlefield during the end step (or, less likely, the cleanup step) after the Wall's ability resolves, its P/T will be boosted by the lifegain from the Wall — but, of course, the Wall can't target the Wurm until your next end step.

And if, for some strange reason, the Wurm enters the battlefield while the Wall's ability is still on the stack, the replacement effect will happen before the Wall's ability resolves, so the counters won't be boosted, and as targets for the Wall's ability must have already been chosen by that point, the Wall won't be able to target the Wurm that turn either.