The idea that Bell would pick Olivia makes sense (although, I was hoping that he would use Walter, as seeing John Noble do Leonard Nimoy would be great).
I don't believe that there needs to be flashy effects for everything, but I do think that the mechanic they used was a bit strange/off. The way I read it was ringing the bell acted as a trigger that alerted Bell's soul to seek out the "soul magnets". In my mind, I want to say that his soul should've went to the magnets as soon as he died, with the bell acting as a trigger to "awaken" him. Either way, I think the simplicity of the entire thing is what makes it seem wrong. "Ring a bell, someone gets possessed?" What seems to bother you is that we didn't see anything that goes into creating the situation, nor did we see anything unusual happen to make it occur. I do agree with that, to an extent. When you consider the way they've done nearly everything else, it seems like a cop-out.