Blender to Ts4s?

Hi, I check the file & the dress doesn't have a cut number in it. The uv_1 is also a bit weird, transfer uv_1 from a similar looking dress not from the nude body or you will have a gap between the leg.
Try this:
1. Find a similar looking maxis dress & export the mesh.
2. Open the maxis dress & append your dress (only the dress, delete the body part).
3. Transfer uv_1 from the maxis dress to your dress.
4. Copy the top body & bottom body and join it with your dress (delete faces that is hidden by the dress)
5. Separate your dress following the maxis dress as reference. If the maxis dress have 8 separate mesh than your dress need 8 separate parts too.
6. Fill in the cut number in S4Studio Mesh Tools, make it the same as the maxis dress.
7. Delete the maxis dress & save the blend file.
8. Import to S4S.

Keep in mind your mesh is triangulated & have to many polygons in it, if you want cleaner mesh you should probably retopologize it first.
But if you're just trying to get the dress into the game try the above step, if it works then you can tidy the mesh more.
Good luck.