That’s a lot of things you wanna do there.
For switching the hair you can simply attach a static hair mesh to the head bone.
For the clothes I would split the character in different skeletal meshes (head, torso, legs, etc.) which all use the same bone hierarchy and switch them out with skeletal meshes which have clothes on them.
One Skeletel Mesh (e.g. the head) has to be the master component and the other ones have to be the slave components, which then follow the master component’s animations.
For facial changes I would use morph targets. You can simply grab the corresponding skeletal mesh inside the Character class (in your case the head) and use the “Set Morph Target” node with the right name and the desired value.