Mod in UE4

Hello all, sorry for my English.
I want to ask some questions about using UE4 for modding and about payment if i have only donations.
So, i want to make mod based on Doom 1 original and community assets.
I want to publish this mod free and open this way, in final exe and in UE4 project.
Is it correct to publish mod in UE4 project? Have Epic Games any problem with it?
And about payment if i have only donations and Patreon, i must pay % to Epic?