It has the effects loop, yes. I guess to use it as an external trigger (for example, sweep the filter on your bass with a drum machine) you'd want to plug the drum machine into the input and your bass into the return jack.
I couldn't really find info on what the "pedal" (expression) jacks did, but I'm assuming one is a CV connected to the LED side of the optocouplers, so that's easy. Not sure about the other one, but any pot on any pedal can easily be replaced by an expression pedal just by using a switching stereo jack.