Mesh is buggy in sims

Hey! You need to delete more body parts under your mesh and close holes at the bottom, neck and sleeves. You did not transfer uv_1, so your mesh does not work with sliders and this lead to glitches with body parts, transfer uv_1 from your reference mesh using options as in picture below. Also your mesh is pretty high poly, I am not alpha cc creator but I think you should mesh in quads and use higher particle distance, then retopology your mesh. But as it's your first mesh this is advice for later when you know what to do