The usual way to assess a patient is to stretch the penis and measure it, or as brassard does, eyeball it. Average size makes average depth afterwords, dilation might make small gains.
I believe brassard uses scrotal grafting. Risks include separation of the graft, necrosis of the graft, stenosis (narrowing) of where the graft joins the other tissue because of swelling or scar tissue formation, and numbness. Unwanted hair is a possibility with scrotal grafting.