1.) Yes, -o will set a desktop dialog so that it is always on top of all other open windows, this means any application not only mIRC windows.
2.) in the dialog table, the first two params for size determine where the dialog is opened.
size 0 0 100 100 ; will open a 100x100 dialog 0 pixels from the top-left corner of your desktop.
size 10 30 100 100 ; will open a dialog 10 pixels in from the left and 30 pixels from the top of your desktop.
