Go with the dress up technique,. You can always transfer the vertex groups from the weight painted body or use it as a collider and do cloth simulation if you have the processing time/power. Deleting any non-visible mesh is mostly for optimizing for game engines.
Yes retopo is important for any deformable mesh. robots that move along joints and hinges not so much but any organic character that moves by muscles you need to make sure that the quads flow evenly much like how skin does.
