nios output can connect to internal fpga bus???

Yes. Nios uses an avalon bus structure that can be exported to the top level of the design and your own logic attached to it, or you can create your own avalon slave device in qsys and use qsys to connect to it.

Start playing and learning about qsys to know about this system. It's a powerful SOC methodology.

The avalon bus structure is defined:

www.altera.com/literature/manual/mnl_avalon_spec.pdf‎

AXI/APB is also available through bridge devices so if your longer term goal is to go ARM, the Cyclone V SOC is a great place to start.

Pete