If you want to really beef up the firepower of your inquisitor you should use three Gun servitors. The first should have the psycannon and the other two mulitmeltas. Alternatively, if you use the heavy bolter option, you can go for three of them, giving nine changes of redemption for the sinners per turn.
If you also get two sages to improve their BS, they can inflict real pain.
Three acolytes armed with bolters, storm bolters or Combi-bolters will add some more muscle to the group.
