Size via yeastcalc.com and make the starter wort with a ratio of 100g DME to 1L water. Time for it to finish depends on yeast age and such. Depending on the size of your flask, you might need to do a two, or three, step starter.
Generally, I cold crash for a full day between steps, or once the final step is done before decanting the spent starter wort and then making a slurry of the yeast cake. Leave a small amount of spent starter in the flask, to get the yeast into suspension.