Is ZERO quests (except for the absolutely necessary ones) and ONLY killing mobs a viable way to level...

Players have flying mounts there. It's much harder to gank people.

get the auto pilot addon

Its not only viable, its optimal

If you're a physical class pick up cooking, first and, herbalism and alchemy, and just focus on leveling those up, this is especially true for a warrior as alchemy will carry your ass with swiftness and rage potions.

Casters don't need alchemy so level what ever profession you want, but the same thing holds true, focusing on professions by farming materials yourself will level you rather quickly

Hunters can do whatever the fuck they want, so just pick up leatherworking so you can make devilsaur leather later

Physical classes you want to focus on beasts and demons when farming, beasts have low armor but high health, but sometimes they're the best you'll get for certain levels, demons are the optimal mob type to farm as a physical class because they have low armor and health, but high resists

For casters, focus on farming humanoids, you don't give a fuck about armor, and humanoids usually have no resistances and low-medium health pools for their levels, avoid demons and elementals, as they usually have retarded resistances, only exception is fire elementals, who are insanely weak to frost, but every other elemental has retarded resistances, even water will have a high resist to fire most of the time.

Classic wow is about the leveling and doing the content. There is no great end game.
Right now the only end game is a single raid that is honestly lackluster (it was originally put together by 1 guy over a weekend).
Stick to retail as classic is clearly not something you would enjoy.

If you're horde, stay in the barrens and just farm mobs till late 20s, then go to ashenvale and farm saytrs till your early 30s, from there go to desolace and farm satyrs there till you can farm the demons near the horde village

If you're alliance do westfall/redridge and farm gore tusks until you're 20, then head to ashenvale where there are tons of beasts, then go farm satyrs and head to desolace

Casters can pretty much farm anywhere there are yellow humanoids to kill, so just do that.

Alternatively, once you hit 25ish, you can farm whelps for pets to sell on the AH, crimson whelps will carry you till 30, 32 if you're wanting to farm them while they're green, same goes for emerald whelplings, which will carry you from 33-40, and dark whelps from 39-45

Another thing to note if you're horde on a PVP realm, if you commit yourself to mob grinding and dungeon farming you'll never have to enter a contested zone to level

as the other anons said classic is the journey NOT the destination

my fondest memories are from leveling, visiting all the zones, getting nice items from the dungeons, meeting cool people that you befriend later

Then go play retail and do that. It takes 5 seconds to get to 120.

Then shut up you whiney bitch

Easily Humans and Undead Mages. Humans and Undeads for comfy zones and Mage because of all the utilities you have. Priest is a bitch to level unfortunately. I cannot think of more comfy zones than Silverpine and Duskwood. In the case of humans however, I suggest Loch Modan instead Westfall and then coming back for Redridge and Duskwood.

Technically yes, but you’ll lose out on gear and money