I can answer by my experience as I'm learning to play with my paladin.
I started using imbuements around level 100 when I was hunting Wyrms. I started using only 1 mana leech (intricate) and it was enough for my hunts, I barely used mana potions and I healed with exura. Later I hunted Hydras and it goes the same.
Around level 150 I started to hunt at SS and Medusa in Goroma, and started using 2 mana leech (intricate). Now I'm level 225 and I'm using 2 mana leech (powerful), and it's enough as I can heal well with the mana I get from mana leech.
So I would say you can start using imbuements at level 100, but you should analyse where you will hunt and if you can handle it without imbuements or if you need some to hunt well or improve your hunt.