If you have IRB to the extent it causes colonization of a softener, it will do the same for an H2S filter and prevent it from working. You will have to kill the IRB.
The H2S/iron filter should be before the softener so the softener doesn't have to deal with the iron, which saves salt, and H2S isn't good for a softener.
It is never a good idea to preplumb for equipment. The plumbing should be done to/from each piece one after the other. And no 3 valve bypasses because they increase the cost and aren't needed if the equipment has its own bypass valve, a 3 way BP causes dead ends and a pressure loss.