Goahead: I strongly disagree with your method of training [but if it works for you then fair enough.]
For anyone who is unsure about back training i would not recommend that routine. One day a week is sufficient enough.
You want a movement that will work your middle back [horizontal row] and an exercise that hits lats more [vertical row.] Then a core movement for lower back [i.e. deads]
For vertical rows, weighted chins or pull ups are prolly better than pull downs, but do what you feel works best.
For horizontal rows my personal favourite is DB rows. I know people who prefer T bar rows with an underhand grip to put their biceps in their strongest position.
Basically, what i'm saying is do what YOU think works best. There ain't nothing worng with a bit experimentation at the beginning. Once you find it, stick with it and keep it the same each week to measure progression.
I would suggest 2-3 sets per exercise and no more than 3 exercises for big body parts.