No problem, i'm not a native english speaker, too
About cut numbers:
Most CAS items are split into more than one meshgroup. This is done to tune each of them individually.
For example, glasses are made of 2 meshgroups: lenses and a frame. The reason the lenses are separated from the frame is to assign a different shader that allows transparency.
Hair packages consist of 3 meshgroups: the original shape and 2 hat chops meant for interacting with hats. When you put on a hat on your sim, the game switches between meshgroups of the hair, showing you the appropriate one. This prevents the hair from clipping into the hat.
Pants can be made of 3-4 meshgroups to interact with high boots. When you put on boots on your sim, some pants will tuck into boots, other will cover them.
Anyway, cut numbers are used to tell The Sims 4 Studio which meshgroup in the imported blend file should replace what meshgroup of the original in the package. For example, when you edit the hair, you want the original shape to have 0002.
To understand what cut number you should assign to what meshgroup, you need to use a reference that is closest to yours item in shape.
And by "closest in shape" i mean skirt length, collar/no collar, sleeve length and volume. Everything else is not important.
For example, your tank top has no collar, meaning it will not clip into necklaces and chokers.
It has no sleeves, meaning it will not clip into bracelets and armbands.
It is not long enough to interact with shoes.
By this logic, your tank top does not need to be split into meshgroups. You can clone either a tank top or a bra.
If I understood you right:
We can append only blend files.
For other files we use Import.
The Sims 4 Studio exports items in .blend format because it preserves rigging, multiple uvs, vertex paint, and cut numbers, which are crucial for functioning of 3d models.
A 3d model we export from Marvelous Designer holds none of this information, which is why we export it in .obj.
So you clone a reference, export its blend, open it, join all meshgroups, save as Your_project_name. Then you import your MD garment in .obj, make it functional. Once done with everything, you join it with the body. After that you append the reference again, this time without joining. You can rename all meshgroups to their cur numbers for your convenience (ref_0000,ref_0001...). Then you start splitting your garment into meshgroups the same way the reference is split. You should give them corresponding cut numbers and names for your convenience. Then you remove all extra vertex groups with this
addon. (Type 0 and click Purchase, it's free. Put downloaded file in Blender\2.78\scripts\addons. Install it ( File - Preference - type remove in the search bar - enable the addon - Save user Settings - restart Blender), otherwise there might be distortions, you want each meshgroup to have the same vertex groups as the one it will replace.
