We usually run 80 blocks, but if the birds are really decoying good we'll go down to 60 blocks. All of my decoys are on main lines.
Are spread is set in the form of a giant "V". The layout is positioned towards the end of the "V". The opening in the "V" is where the birds usually start to land, giving us a 15-35 yard shot.
If there are mallards or blacks in the area, we will attach one mallard deke at the end of each main line. That is usually enough to coax them in for a landing.
We also carry a white flag in the layout boat. That helps pull birds from far away distances. More decoys is not always better. We try to get by with the least amount, but I have set out over 100+ blocks before. If you are killing birds with 60 dekes why bust your butt to put out another 40 or so. In the layout boat we hardly ever have a problem decoying birds. We also kill geese out of it too.
I have all my diver blocks painted black and white. All black heads and a brite white bodies. Some decoys I have painted all white, they seem to have more attraction and flash to them painted that way.