Ow, my head hurts. But yes, if only visiting/returning from the west, you neither enter the WZ, nor do you need a wag bag.
As for the original hike being planned, IMO the n->s route is preferable. Going down Carillon, up MR and down Discovery is better than the reverse.
Also, taking your time going up Shepherd helps acclimatize for the rest of the trip. It's also one of the more scenic trails - the canyon is immense.
Note: Have another aspirin: "From the west" means the JMT, not the Carillon approach and MR. To do this, you definitely cross the Crest (over Whitney/Russell or Russell/Carillon) and enter the Whitney Zone, which you are in until you cross back over the Crest at the Notch at the top of the MR chute. You need the Visiting Whitney permit for this route. You also cross back into the zone to take that top section to Switcher 99 for the use trail to Discovery.