That sounds like excellent advice you got from Rob. You can call or if you're close enough, go to Lancaster Archery. Those guys are great and really know their stuff. I dickered in target archery years ago just as a hobby. My bow up was very similar to yours but I just can't remember what spine the arrows were as I bought the set up used and the arrows came with the bow. I do know that at 20 yards using a thumb release I could cluster my arrows in the center of the bull with little difficulty.
Good luck on your future.