It's doable, but most likely faster to mix and match the non-collection / easy collection quests into your grinding. Are your 3 warlocks Recruit-a-friend linked? If so you should have few if any problems skipping collection quests from 1-60. If you they are not RAF'd then you are probably going to want to do some of the collection quests along the way, take a look at which ones will open up xp rich quest chains. For an example the Stromguard horde series in Arathi Highlands has a step that requires you to collect x signets but in the end has some pretty massive xp boosts once you get beyond that step.

For 61-70 you're really going to have a lot of grinding ahead if you skip the collection quests and are not planning to group with your 3 x locks for instances.

-Stav