seeking suggestions on adding external hardware buttons to execute macro/scripts

I'm a noobie looking for suggestions on how to add external hardware buttons that can control any functions on a Kocaso Mid9200 tablet running Android 4.2.2. The basic goal is to push an external hardware button and play a favorite radio station in one app, or another hardware button to stop playing that app, and switch to another app and play specific favorites within that app. I'm open to writing macros/scripts that might invoke the desired function then linking a specific external hardware button to each different script. The tablet is rooted. The tablet is cheap and does not have either Bluetooth or NFC (so external NFC buttons like the Pressy or Dimple are not an option), it only has a USB port.

I've placed an order for a PCSensor Key Fere external programmable USB keyboard and plan to build macros keystrokes into that device to start the process. I've also started to look at using the External Keyboard Helper app to tie a keystroke to invoke an app. But I could use help in figuring out how to write a script/macro that could navigate within an app and select, for example, one of several favorite radio stations in the radio player app, and start/stop that station in the player. Ultimately I'd like to push one button on the external keypad, and have it invoke the desired player app, navigate within the app to select a specific station, and start that station playing.

Any help would be appreciated. Thank you.