Bricks, Masonry, Asphalt and Concrete - wood retaining walls, drainage

HI,
I am building a series of terraces in my downsloping back garden and am looking for some drainage advice.

I am building 4 retaining walls, each 3ft high and 20 ft long using pressure treated 4x4's and 2x12's running horizontal to the ground. I was wondering how much drain rock backfill I need to use behind the wall for drainage. Is 4 inch deep starting approx 4in below the bottom 2x12 board, up to approx 6in below the top of the 2x12's sufficient or too much?

Do I need to use a preforated drain pipe at the bottom of the gravel backfill to slope the water away.

Should I surround the drain rock on 3 sides with landscape fabric (ie on the soil side, the board side and the bottom)

Are 4x4's sufficient?

thanks
derek

_______________ ________________ _______________
__________ _________________ ____________________
________________ ______________________ _________

You could probably stagger the 4x4s like that on top of each other to let the water through. Use #8 gravel behind the wall the way you described. The french drain and cloth aren't needed in my opinion.