It appears that this addition will be attached to your house, if it is, the sub-panel does not need a main, if it is a detached building, it may need a main, see 225-31, 225-33.
As for the closet issue, depends how you feel about your mother-in-law and if the addition is attached to or well separated from your house.
![[Linked Image]](https://www.electrical-contractor.net/ubb/biggrin.gif)
Tom