First of all i love Sankey Diagrams but never get enough opportunities to use them.
The chart library is based on d3.org sankey diagrams
The data format it needs as per that page is:
{
"nodes":[
{"node":0,"name":"node0"},
{"node":1,"name":"node1"},
{"node":2,"name":"node2"},
{"node":3,"name":"node3"},
{"node":4,"name":"node4"}
],
"links":[
{"source":0,"target":2,"value":2},
{"source":1,"target":2,"value":2},
{"source":1,"target":3,"value":2},
{"source":0,"target":4,"value":2},
{"source":2,"target":3,"value":2},
{"source":2,"target":4,"value":2},
{"source":3,"target":4,"value":4}
]}
As for how many nodes it can support, I'm not sure there is an upper limit, though I suspect you would quicker be constrained by the page space/browser memory limit.