Avalon_bus_to_extenal_controller

Although you know your product better than anyone here, wouldn't it be more cost effective to use a Nios instead of an external 16 bit microcontroller taking up board space and extra cost? You may find the 'e' core does what you need and small enough to justify the change.

Anyway ...... your first post is pretty much what you would want to do. Your external signals will need some sort of glue logic to adapt them over to Avalon master signals then all your peripherals in SOPC builder connect to the Avalon master interface. So the real work is making sure you create a bridge that obeys the Avalon spec.