Troubles with mesh.

Hi. I suggest you to postpone finishing this project, watch a different tutorial ( look for the one that is recent and where the author does not tell you to download Blender 2.7 ) and make something simple like a skintight top, not for the sake of sharing with other people but learning.

1). To avoid the issue you're experiencing, clothing like this must be made with arms down;
2). Your mesh is way too high poly. Most of it comes from side and inner geometry. You must export the mesh as thin from MD. The inner geometry is needed only in places where it is visible. No one would be seeing inner side of sleeves, so they are not needed. The most complex maxis meshes generally do not go past 10k polygons, the game does not require a strong machine and is not optimized to render an almost 100k mesh. You are fortunate to have a good graphic card, but for most other people the game will just crush. So if you're planing on sharing your cc, you need to be keep it in mind.
3). An accessory jacket should not come with the body. Clone any accessory, you'll see that they have no body attached to them. What you are seeing under the rig is not imported.
4). Do not join the garment with the body ( if you're making something that should come with it ) until you'll make the former fully functional, so at the very end. The weights and uvs do not transfer right to the body and you'll end up with distorted fingers
5). You have uvs in the area meant for shoes ;
6). The mesh is vertex painted with the wrong color, it should be 00ff00. Could you please link me to thea tutorial you watched because lately we've been seeing people vertex paint with this specific hex code. I've found the original post but my guess is there is a tutorial by someone else who saw that post;
7). For the reference, do not clone something that is vaguely the same in shape, choose items that are the same in length and have the least sculpted details. For this jacket you can just transfer weights from the lingerie set or a swimsuit;
8). You can put symmetrical patterns on top of each other to save space