Level 1 should be easily doable.
You can also do Level 2 - but it'll probably won't be that easy.
I say - what's the rush? Go, gather some XP and loot and complete the whole keep post Underdark.
However, if you do the Keep while still in SoA, you'll miss out on all the NPCs Keep-related interactions, so you might want to postpone the Keep until you reach ToB.
Why BioWare chose to restrict the interactions to ToB is beyond me...