Create Game With in-game character designing like sims?

i want to create a game with in game character designing like sims ? How do i go about it , what challenges will i face.

I do not think you would have trouble with skin color, hair and clothing as you can just attach them to the mesh.

I think the hardest will be altering body parts like hip size and alike as I do not of a way of doing that inside the editor. Not saying you can’t, I just do not know how.