SCS coordinates are mandatory, this is the central coordinates system in Brainstorm, anatomical surfaces and sensor positions are defined in the system of coordinates.
Therefore you need to define NAS/LPA/RPA.
To use default positions: simply compute the MNI transformation for the MRI of your subject (process "Import > Import anatomy > Compute MNI transformation")
Subjects are created automatically by the processes when importing the anatomy.
"Study" folders are created automatically when importing data to the database. If you don't import data, you need to create a folder manually with db_add_condition.m. This will give you the iStudy you need.
(look for examples in the code)
https://neuroimage.usc.edu/brainstorm/Tutorials/Scripting#Reference:_File_manipulation