Does seller's size chart work well for choosing size?Does it fit as expected ?

For me, robe fit to size as expected and has decent amount of stretch too, but the bottom portion of robe was awkward and did not wrap around fully even though the upper robe fit beautifully with a casual drape and flattering amount of room to spare when belt was tied. You might have to order up a size in order for the robe to close fully below the waist

What size in this for a 38 D bra ?

It is very cheaply made and sizing runs very small. Personally, i would not buy this robe. I bought it and donated it immediately.

How do you measure the length of the robe. Is it from the shoulder seem to the hem

I am not sure but I am 5.5 and it falls at my ankles. :)

What's the material of this long robe?

I bought the solid black and Floral #1. They are different material. The solid color robe is made of 95% cotton and 5% spandex. The floral robe is made of 95% rayon and 5% spandex. They are as advertised and good quality. Very soft and comfortable.