Okay Dan, I will send you my complete Reaper file so you can see how I have mine set up. Of course there will be a lot of my Toolbar actions that won't work because many of them require scripts. However it might give you an idea of what you can do.

Incidentally, I just tried this with a fresh Reaper install, and Reaper crashed when I set up a loop with the action to stop at the end of the loop being on. This is with BIAB showing.

Dan, are you familiar with the actions in Reaper at all. Use "?" (Shift+/) to open the actions. Then in the filter box, type "Transport: Toggle stop playback at end of loop if repeat is disabled". Then assign a shortcut key to that action.

Are you familiar with the "SWS" extension and do you have them installed, although you don't need them for this.