How wide would you recommend the green space to be (ideal width)? is 4ft enough for plants/greenery? Will 3ft do?

Steve,

The wider the better, no 3 feet is too narrow. 4 ft. is barely adequate, but if that is all the room you have, it will be fine. Be sure to consider the wall / border width and don't include this dimension as part of the overall planter dimension. Roots need some room to spread out and relax.

to be clear. With 3ft or 4ft I am referring to the width of the planter space. this excludes the fence/wall. Its purely the space available to plant trees/bushes.

If you aren't planting a large tree in the space, 3 ft. is fine. The dimension that looks right will depend upon the proportion of overall design. Work with the space available, just give any trees you may be planting space for them to thrive.

This looks great, I would love to have something like this in my yard. The pool with the plants looks awesome. Does it take long for the plants to grow, and give privacy? http://jklandscape.com/