Do the math on Storm Bolters.
Flamers work pretty good with Divine Guidance.
If you have a squad of 10 deploying from a Rhino you should be asking yourself why you don't have a Heavy Flamer and think seriously about a Flamer to go with it.
Heavy Flamer / Meltagun or dual Flamers will be beautiful.
I would drop the Inferno Pistols for Flamers. With Divine Guidance you will kill many, many more marines and about the same number of Terminators. Any vehicle in charge range of your Eviscerator is dying anyway.
Immolators can only be taken for units strength 6 or less.
Having said that Celestians are rarely worth their points and Dominions and Retributors are marginal choices, keep them cheap.
Most people leave their Veterans with Boltguns, the extra attack will not win any combats and the extra dice rapid firing will help you.
Rosarius on the Cannoness is unnecessary, she can get a 2+ invulnerable save, especially if she is alone and rolling on her leadership.
I'd be tempted to go an Eviscerator on the Cannoness, just because she will survive to use it and she may as well crack open a tank or two.
Vehicle upgrades apart from Smoke and Extra Armour usually don't help much.
I've converted my four Immolator kits to really cool looking Rhinos.
Playtesting will probably get you there, too.
The most viable way of fielding Immolators is with a minimum sized Celestian squad with two Meltaguns.
You're certainly barking up the correct tree.
If you'd like to see how tournament builds usually end up:
http://www.40konline.com/index.php?topic=144230.0
