The documents included with your development board along with those included on the Altera website like:
http://www.altera.com/literature/hb/nios2/edh_ed_handbook.pdf http://www.altera.com/literature/lit-nio2.jsp will provide you with the knowledge you need.
As far as your question of how long it takes. For those who are experienced with FPGA design and the NIOS, a project like what you are describing can be done in weeks or even days. The power of the NIOS processor is that it allows you to develop and debug very quickly. Using the embedded processor can easily shave months of work off your design time.