Build the framework of a sandbox videogame in the Unreal Engine

Hey freelancers, We're storytellers, not game designers, and we need some help. We're looking to create a sandbox MMORPG with elements of magic, spellcasting, binding, exploring, and crafting; as well as the ability for players to create their own maps/scenarios. (Think Citadel meets Roblox) This is the first phase of the project, we'd like the functionality to be there, then we figure we could add the skins & graphics later? We believe the unreal engine would be ideal for our purposes, but aren't opposed to other engines or solutions if easier/better options are available. Kept this short and easy, more details if you're interested. Thank you for your time Nik