Update here 
I have made a “Let’s Create” video inspired by GaimeDev.
I recreated Ezreal with the Multiplayer Combat Editor tools (minus the basic attacks and the passive).
Here is the video showcasing the whole process (50 minutes) but timestamps are in the description if you’d like to just check the end results
My experience highlighted few things I needed to improve regarding the skill creation workflow.
It also made me realize I did not think about Passive skills at all (it did not cross my mind whereas I’m a moba enthusiast, I feel bad :p).
I’ll surely not add them now without prepairing their addition properly therefore I’m likely to add them after the release.
I’m going to fix the few thing I noticed and I guess I’ll be packaging an example project for you guys.
In the meantime, have fun in your projects everyone
EDIT: Everything seems to be working fine in 4.16 without any efforts. It’s looking promising