My suggestion would be to start here and the suggested Follow-On Courses
http://www.altera.com/education/training/courses/oqsys1000 a) NIOS is a 32-bit microprocessor IP core
b) Qsys is the tool you use to chain together IP cores and specify a system
c) Quartus translates the Qsys output into an FPGA image you can program in your board.
d) After your image is in your board, you use gcc/g++/gdb/Eclipse/yourcreation to execute software in the NIOS you put in your FPGA.
As far as purchases go, you can get quite far with the board you have chosen and whatever computer you already have.