selecting I/O modules

Hi everybody, I have been asked to convert a relay logic system into a SIEMENS PLC system. But I got stuck in the selection of I/O modules and CPU for the system, Since the old system contains NPN type sensors.

I'm new to this site and also to the field of Automation,as you see and please guide me to finish the projcet.

The NPN-PNP-question is asked many times in this forum.

Maybe you can use this:

http://www.simcotech.com/smartplug.htm