I think you could drop the roasted barley. I used 8oz chocolate in a similar brown and it makes a very nice color, leaving a nice roasted flavor but not over powering. You could consider upping the crystal malt, but with the S-04, you will probably leave enough residula sweetness for some body.
I think the IBUs are fine. I have used Vnaguard so I cannot comment on that. I used Centennial and Cascade, it was great.