Your best bet is to follow as precisely as you can the application procedure.
You don't get bonus points for having a fourth reference.
Most applications will, require you to essentially submit your CV in one form or another. Some will ask for it explicitly. Others will have you fill out a form that contains about 90% of what would typically be on yur CV anyway. So if you're asking whether it's a good idea to put one together at this point, the answer is yes.