Stone of Change - Eldritch Rituals Cookbook

[Borror0]

Priest would like to build something that ends in EDP ...

a) Do we think that the final upgrade MUST be EDN+EDP to make that happen?

Yes, if youvary the Essence or the Gem, it fails.

b) should I have any concern starting out MEN/MEP or MEN/MOP or MON/MEP or MON/MOP?

Nah, if one of them work, they'll all work.
Maybe, that going -/+ won't work, but that is no one has tested yet...