12m is the length I posted when this last came up. I think 11m will do but 12m is best so bits can be snipped off. Not sure about dynemma because of the sharp turn at the top and whether it likes going through cam cleats.
I use dynemia or spectra, but I use 4-6mm depending on what I can get my hands on and have done for many years with no problems (so far). I find these bite better in the cleat than a 3-4mm rope.