1. The main objective differences are price and specifications.
For the spec of N1, please go to
http://www.kyoceraimaging.com/product.asp?itemnum=141000
For that of NX, please go to
http://www.kyoceraimaging.com/product.asp?itemnum=141010
However, subjectively speaking the above said differences might not even be of your concern. For example, in case you don't care about the greater weight of N1 and the price difference, it might be better to go for the N1. Another case which might leave you with no choice but to buy the N1 is that you need the multiple exposure function.
In practice, I guess NX is sufficient for everyday photography. But as the N1 are targeting at the more demanding photographers, it surely has an edge.
You might provide some information as to your photography. I suppose many of the experts except me will eager to give their invaluable advice.
2. C/Y means Contax/Yashica mount. There has been (probably had been) a full and complete line of C/Y mount lenses available for a series of Contax SLR cameras. The C/Y mount is not compatible with the N mount. C/Y lenses do not support auto focus (but one of the C/Y cameras do.)
Generally speaking, people talk about Contax cameras (since 1974) with reference to the series to which they belong:
1. N series for the one introduced in around 2000 with AF and MF. The lenses are specifically designed to be compatible with digital sensor in digital SLR(s).
2. C/Y series means the line of SLRs and lenses since the RTS (Real Time System) in 1974.
3. G series means the line of rangefinder cameras since 1994. It is like a P & S camera with a complete line of interchangeablae lenses. G cameras can use C/Y lenses through the use of a GA-1 adaptor produced by Contax. It supports AF and MF (without the need of focus knob).
4. T series mean the 2 lines of P & S cameras (TVS and T).
5. C645 means Contax AF 645. A line of AF SLR for the 645 format (medium format). All of the C645 lenses can be used (through the NAM-1 adaptor produced by Contax) on the N cameras with the preservation of AF capability.
Please experts here correct me if I am wrong.