How to determine if I need custom components in Qsys/SOPC or not?

Basically, what I want to do is: FPGA receive signals from Nios ii and pass these signals to Mosfet switches (does it mean that since Mosfet signals are external components not on the board, so I need a custom component for this purpose?). Then, FPGA sends voltage and current signals from ADC to the Nios ii.

I just don't know how to determine if I need custom components, if I need, I know how to set those chipselect, readdata, writedata, conduit signals etc where I can set like when readdata is activated, nios ii is going to read data from FPGA. But if no custom components are created, how do we perform this readdata for instance? I hope I made my question clear this time, sorry.

FPGA: receive signals from Nios ii and pass outputs to the external circuit

Nios ii: receive signals from FPGA's ADC, do all the processing tasks such as arithmetic operation, sort ascending/descending, comparison if-else etc, pass outputs to the FPGA