I can't answer number 1, but for number two, you will not hurt or damage anything. I need 46 node per string, but i'm planning to start each string either on the even hundreds or fifties to make programming easier, at least in my head.
All sscs receive the entire pixelnet universe and select which channels to use based on how you programmed it.
The only time that programming the ssc for more nodes than there are will be a factor is if you reverse the order of the nodes... if you have 45 nodes and tell the ssc that you have 50 inreverse order, the node on the far end will be #6.
RM