I do hope you at least raid hardcore mythic progression, because if not, why would you use for example expensive pots and augment runes that drive the consumable expense so high?
I mean people can augment and pot old war in lfr if they wish, but then they wouldn't treat it as "crippling" only a luxury they can easily afford, right?
First of all, there is a point where you don't need so many WQ on main (maxed AP on mainspec, stockpiled enough OR, outlevelled all the gear rewards etc.), so you just cut down on those while devoting that spare time to alts. Only chop the emissary cache for your legendary BLP.
Second, it's easier to rotate alts - stockpile 3 emissaries and do them quickly on 1 alt 1 day, next alt next day etc.
Another option is to always do "fast quests" on alts like the ones that require you to kill 1 mob, use group finder to chop those WQ even faster, always skip the super nuisance WQ like shitty respawn rate mobs (if you know these imps on top of the mountain in stormheim etc.)
Prio the OR reward quests and gear on fresh alts, don't bother with AP until they have max AK, you can get few early tokens from Suramar opener and emissary rewards that will put you at ~20 traits if you buy the AK20 book, but no point prioritizing AP rewards since you're earning them at about 1/3rd the rate at this stage, better get gear and OR.
Only prob with cherry picking quests are travel times, I usually do some house chores or check news while on the flight path so I don't sit and stare at the scenic route.
A supplement is to pick the order hall improvement to snatch 1 WQ for free every day, you can use it on OR quest. Can't remember which classes have it, but it's easily checkable on wowhead and it's about half of them. I know I have it on DH, Warrior and Paladin, can't remember the other 3 because I don't have these classes yet.
On Druid specifically, always keep Broll and always send him on missions - his passive adds up when you want to save resources. I don't like him as bodyguard anyway because he always fucked up my shadowmeld tricks. Rather use the Cenarius guy it's actually really good damage / healing for these wardens quests.
Don't send the raid / dungeon cache missions they cost fuckton of OR, unless it's an actively played alt that has good quality raid caches (not lfr or some shit).
Put bloodhunter shoulder enchant on as many characters as you can to get extra backup supply if you run out of resources. There is even a trick if you have any levelling alts you can enchant bloodhunter on a heirloom from a char that has rep then mail the heirloom to the alt, yes, the alt has to level with 1 shitty ilvl piece as the heirloom won't scale, but if it's a class that doesn't have too hard time levelling it's extra bloods for free.
If your alts happen to be profession-less, pick enchanting, free source of extra bloods from DE. I've heard skinning is another recommended profession for easy bloods, but since leathers aren't very profitable, I'd probably opt for herbalism instead. Takes some time to discover rank2 but it's again free stuff while you roam around doing WQ.
All these are pretty simple / common sense, not sure if there's any secret strategy anyway except "buy OR for bloods" and "stop farming OR on main do them on alt instead".