My current playthrough I did things in this order:
1. Recruited Shadowheart, Astarion, Gale, Lae'zel
2. Did stuff in that area like kill the mindflayer and find the Harpers' stash
3. Picked up Withers from the crypt
4. Went to the grove, explored there, found Nettie, agreed to rescue Halsin, talked to many NPCs (including Auntie Ethel who told me to come to her house and she'd help me out), initiated the "Investigate Kagha" quest
5. Dealt with the goblins in the cave next to the grove, talked to Edowin/Andrick/Brynna, went to the owlbear cave and saw the shrine of Selune as well
6. Picked up Scratch
7. South to the swamps, found evidence of Kagha's misdeeds
8. Went back to the grove, confronted Kagha, stopped the ritual, etc.
9. Back to the swamps, killed Gandrel, fought the hag and rescued Mayrina
10. Then I went up north and fought the gnolls, did the missing shipment quest, Waukeen's rest, the tollhouse
(I just... haven't been recruiting Karlach or Wyll because their stories/characters are less developed and I like to have a smaller party.)
I see the tiefling party as kind of the culmination of all of the events of (the first part of) Act 1, so I saved the Blighted Village and Goblin Camp for last. It makes sense to go to the creche or Underdark right after the tiefling party based on what Halsin tells you.
So, if I'm already level 5, I go to the creche first. Then I hit the Underdark last because I like to take the elevator in Grymforge up to the Shadow Cursed lands. I didn't have much difficulty doing things in this order on balanced mode.
