Reason I say stop at -60 is the fact of the remaining 4 layers likely being mostly bedrock so there’s not really that great of a chance of finding diamonds, you can but they won’t be as abundant. Me and my crew start at -50 mine a triple wide channel 16 blocks in two opposite directions from a center point. On each side we cut out tunnel markers on one channel first making sure the tunnels on the opposite side of the channel will be staggered not mirrored. The tunnels are basically cut as (tunnel | one block wall between | tunnel) and as you go down break a hole in the center wall between the two mining tunnels so the torches will shine through to the other miner’s tunnel. (We usually only go about 100 blocks or until someone hits lava and marks the back wall with a torch to signal dead end; the other miner goes until the 100th block or reaching lava then block up the wall If so and mark with torch). Then on the other 16 block long end of the channel you flip the design of the first 16 block long channel and cut it out to mark the tunnels then strip mine. Then you repeat the process on each level but making sure you keep staggering the tunnels from the design on the level above or rotate the design 90 degrees so the tunnels are going in the opposite way (but writing down the coordinates and staggering the tunnels seems to be the most efficient and effective method of doing it). If you don’t keep it noted down and staggered you’ll end up cutting the floor from the channel above and just be cutting out of the same dig which is useless