Welcome back to the game. Always good to see more Witch Hunters
Cleanse some heretics for me.
Some comments on your army choices:
Cannoness 181 points: She is pricey, and something a lot of SoB players don't realize is that a Blessed Weapon is a two-hander (which means you might as well leave the Plasma pistol at home). Also not unimportant as you're planning to add her to a Seraphim squad, the squad loses it's Hit and Run rule when you do. Given that you have some points left, it might be worth considering to change her out for Saint Celestine ( just not sure you HAVE her, or any models beyond those listed, though you might get away with a Counts As?). As an added bonus, you'd then be allowed to bring a Blessed Weapon for your remaining Cannoness as the Ardent Blade doesn't count against the 1 / army limit
Second Cannoness, as you're obviously accepting that she's likely going to get into Close Combat, I'd suggest grabbing a Celestian squad either as a retinue or elite choice (and maybe mount them all in an Immolator). For a handful of points difference, Holy Hatred and the added WS will likely be worth it if CC happens. Another amusing option ( well, for you, not so much for your opponent) is adding her to a large Battle Sister squad and bringing Litanies of Faith to cheat on a Faith test at a critical time, but even if you pull it off well this'll only work on any given opponent once
Litanies of Faith may well be worth it in any case, as it's effectively a free Faith point.
That's a lot of Sisters... I like that. Not sure whether it'll always be effective, but it's going to look awesome
I'm not sure you need quite that many Books or Melta Grenades... You may want to reconsider their rides as well. The Dozer Blades are only going to be worth it if there's a lot of terrain in the way, and 10-point Blessed Ammunition seems wasted on the Rhino's single Storm Bolter. I'd suggest dropping both those upgrades. Alternatively, add a Pintle-Mounted Storm Bolter so the Blessed Ammunition has twice the impact. Extra Armour is always good. Hunter-killer missiles, while expensive, might prove amusing.
Overall, the Sisters' version of the Rhino... kinda sucks (Compare to the 35-point SM one, which has Smoke/Searchlight INCLUDED in that and has an additional firepoint). Note that you can drop a Battle Sister squad or two in favor of smaller Celestian and/or Dominion squads and mount those in Immolators, but I'm not sure whether you've got models for those. Compared to the Rhino, I've always considered the 15 additional points to get the Twin Heavy Flamers a good deal.
You've got extra room here, so it's possible to break up the Seraphim into two squads and get an extra VSS and Faith point. Two squads of Seraphim can be in two places at once. Admittedly, that also means they can be gunned down a little more easily if you're not careful. I'd say think about it and go with your gut feeling.
Yay Exorcists. Easily your best bet for killing off scary things at a safe distance (excluding Land Raiders, sadly. Bit of advice, have a plan for dealing with an SM LR Redeemer).
Retributors, you want the VSS for the Faith point, anyway. The fact that she can bring wargear is just a bonus. Not much to say about them otherwise, just make sure to set them up in a nice bit of cover.