I use under 6 long rest for EA. From the beginning, you can go until L3 and the Druid Grove and Owlbear.
Rest after Blighted Village + Wood Woads + Redcaps + Hag Lair.
Rest after Gnolls, Tyr Toll Bridge Brigade, Waukeen's, Githyanki.
Rest after Goblin Camp is cleared entirely.
One rest in half of Underdark.