[Solved] How to have a nice uv

Hi. As of right now, the mesh is unusable.
Retopology has multiple purposes( none of which are fulfilled at the moment):
- low polycount to not put a strain on the game engine and negatively affect the performance. It should be as low as possible while preserving all the details that cannot be preserved through textures. Wrinkles are preserved through textures, overall shape and big folds - through mesh. Right now your mesh's polycount is 16 times higher than that of Maxis's most complex meshes. So high, it exceeds s4s polycount limit, so it cannot even be imported;
- reasonable edge flow for good shading. The edges should flow along big fold;
- supporting the functionality. In places where the mesh bends, there should be edge loops. In places where the mesh expands, there should be circular edge loops;
- (s4s specific) there must be edge loops in the same places they exist on the maxis body.

These steps should be done differently:
- in MD use quadrangulated avatar with no doubles;
- when you're done sewing, subdivide the avatar, increase the particle distance of the garment, simulate for a minute or so to create wrinkles in places where they should be. This will be much faster an easier than sculpting them;
- once done, export the garment, naming it "high poly version" or something like this. You can bake textures from it to your low poly garment later;
- MD 11 has an amazing and easy to use manual retopoly tool that will provide you with results zbrush cannot ( because zbrush does not know where the garment should bend or expand). So once you get the desired shape, you can start retopologizing it. If your computer will struggle to do this, you can reduce the particle distance without simulation ( so that the shape remains unedited);
- once done, apply the retopology and export as "low poly version";
- in blender adapt the low poly version ( clone a similarly shaped garment, export, open, import yours, close holes and unwrap created geometry, transfer weights+uv_1+vertex paint from the reference, remove all areas of the body covered by clothing, join the body with the garment, make uv_0, assign cut). Check in-game;
- once happy with how the mesh behaves, bake diffuse and normal map from high poly to low poly

In Md, fabrics behaves akin to the real world analogues. if the top is tight, there's no wrinkles.

If the top is loose, there are wrinkles.

Your top is tight, so logically there should be no wrinkles, but if you want to create them, you just need to make the top a bit looser by adjusting the shape of patterns or shrinkage weft/warp. You can also change the fabric type, but that works well only with properly fitted clothing ( like real world patterns)

Those are made in MD. Those examples of clothing are just not tight.

I would advice you to not create yourself problems on the learning path with zippers, wrinkles and the likes. It will be harder to learn the basics with them. Just make a simple top first, adapt it successfully, then make whatever you want. You can skip the whole retopology step for the first item, just make it in quads and low poly.