I can see holding off on specific levels of essence since we don't know the scale but we do know a few things about essence.
1. Is important to the channeler for imbuing objects / entities
2. Is used in some spells
3. Determines the Channeler's power level when used in conjunction with other potential stats.
4. Doesn't serve the same purpose as mana.
5. Is expected to be nonrenewable or semi-renewable.
There is more than enough data for general speculation on essence levels dealing in percentages but any actual numbers (EX: 5 miles of land needs 34 essence to be restored, etc) is impossible to estimate at this point.