My personal experience is that lining up fletching is neccesary. Thats just me I guess. About the o-rings... I had the same problem, I glued in my inserts before I screwed the broadhead in and the heads wouldn't line up when they were all the way tight. What I did was back them off a bitt to align them and made sure they were balanced and shot. The problem with that was after the first shot in the block the broadheads would turn and the balance would be off. Also I've become afraid that I might lose a blade. A friend of mine said I could use some locktight on the threads and set the broadheads in and that would work. That would keep the heads from moving but I still might lose a blade or two. Best thing to do is, screw the broadhead into the insert and then glue the inserts in.
Good luck,VH