Cut number issue

Hi. You don't actually need to split your dress for the following reasons:
- most dresses are slit at the bottom to tune these meshgroups to hide parts of tall boots that are above the ankles. This prevents them from clipping into the dress when the sim walks.
Your dress has openings on the sides, right? So if the game will hide the upper half of the boots, you will actually see that that part is missing.
- your dress is barely affected by foot bones, so it is safe to delete them. Deleting foot bones eliminates the possibility of severe distortions. So even if did not have those openings, you still could get away without splitting the mesh ( it is not tight enough for the boots to clip )

But I have a different issue with the dress. Is it meant to have transparency?
If yes: the skirt uvs must be in the extra space for tops and bottoms where there is no skin. Where they are right now there will be skin. And all parts that are meant to be transparent have to be separated into a different meshgroup ( to assign a different shader to it );

It seems that you transferred the uvs from legs, not a skirt, so it's best to re-do that, but it will not magically fix everything. This is the con of making dresses with folds like this. I would know bc I have a similar one and spent weeks manually editing weights.
No maxis dress has any details (folds, buttons, bows, etc) in the "between-the-legs area" where the right vertex groups meet the lefts ones. The movement during walking is very sharp, whatever is in the gets stretched too much.
You can try manually editing them so that they meet somewhere in the crease like i did