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.
If you are having problems seeing the CAPTCHA, please clear your browser's cache and cookies and ensure that you do not have any browser addons or extensions that interfere with the display of the CAPTCHA. Then, close the CAPTCHA window and click on the register button to open the CAPTCHA again.