Well rough guide.. finish act 1 lvl 8
Act 2 16
Act 3 18
Final fight 21-22.
Theres a learning curve in DOS2.. start with classic (or whatever difficulty you like), then if you like increase difficulty.
And enjoy to journey!

BG3 Modder: https://www.nexusmods.com/baldursgate3/users/55895062?tab=user+files