Hi.
The dress has no uv_1 map, only the body. How to create it is explained
from 2:37 to around 4:00. What it does is explained from 00:00 to 00:25.
The size of UV islands in the uv_0 map defines the quality of your textures.
Always put UVs in the place that is left after deleting covered body parts. I do not recommend putting anything ( unless you absolutely have to, which is not the case here ) where the dress' UVs are right now because many creators do and that may lead to texture overlap between items.
The dress is too high poly. It will slow down the loading time both in the game and in s4s. You can reduce it by raising Particle distance in MD or
retopologizing it.
Export meshes from MD as thin, not thick.
Create in quads instead of triangles. This way you will get a smoother mesh that has lower polycount.
There's no need to leave this much space for legs. They will not be seen but you'll be wasting UV space for them.
Vertex paint dictates how much sliders and body parameter alterations affect the mesh. Skin-tight areas of the mesh should be painted with 00FF00. The bottom of the skirt should be sampled from a reference that is the closest to your mesh in shape. Here's an example of how to paint a dress:
Start by painting the dress with skin-tight 00FF00
1). Switch to Vertex paint and enable Face Selection masking for painting;
2). Press A to select everything unless the wireframe is already pure white like in the pic;
3). Click on the white color;
4). Type in 00FF00;
5). Paint - Set vertex colors.
Then sample the very bottom of the skirt that is closest to your mesh in shape
1). Switch viewport shading to Bounding box;
2). Choose a dropper;
3). Sample the color.
Then paint the bottom of the mesh:
1). In edit mode disable Limit selection to visible;
2). Press B and select the mesh kind of, um, in the middle of the pelvic bone? like I did in the pic;
3). Switch to vertex paint. Enable Face selection masking for painting;
4). It remembers the color you sampled last. Paint - Set vertex color;
5). Press A to deselect, press A again to select everything, Paint - Smooth vertex colors.
You should not upload the same blend to all LODs because it will be harder for your pc to render it in-game.
How to make LODs is explained here.Also, I hope you figured out that you should use Clean tool after transferring weights to prevent it from flying.