Just keep playing the game, explore as much as you'd like.

find the Underdark access in the Blighted Village - do more side quests

Hey, that's nice. Hope you are enjoying the game. Try going to the underdark first and then the githyanki creche.

i'd suggest exploring around a bit and examining the available paths before advancing to other regions like the creche or underdark - you may be missing some neat loot, sidequests, or even companions.

1700 hours in and I'm still discovering new things.

ACT 1 not counting the gith creche will get you to at least level 6. Level 5 is a major level because it unlocks your 2nd attack on most martial characters or double cantrip damage on casters and so on. At level 5 you can do any of the fights in act 1, but 6 will be better against 2 or 3 of the worst mini-bosses.

There are a few side quests in the Grove. However, some of them have to be done before defeating the goblins.