1px thick, standard round brush, for hard details (such as the stripes and the gold detailing and such) on the size variation pen pressure setting. For regular shading I have the opacity pen pressure setting.
To get tiny details, it's more a case of drawing it, then going round it in another colour, or erasing it slightly. so draw it bigger than need be then reduce the size (this is how I get the eyeliner, because black is a bitch and goes on all thick and blobby)
draw and erase is how I pretty much do everything... like for the folds in the skirt I draw them thick in the dark colour, then go over the edges in the paler colour to make them thinner and more controlled