Depends on the farm I'm doing this place we have done recently doesn't have warrens that are that big,, the largest was one of around 60 holes,, a few week back and we put 6 in ,, there was 3 of us and each had 2 .. But most of the warrens are under 30 holes ,, so two are plenty most of the time
One or two of the other farms have big warrens on banks stretching a hundred yards or more ,,, and again we will start one end with half a dozen or more ferrets,, and move along,,
As for sexes I use both ,,, but for the last year or two the best ferret in my court is a hob of a smallish to med