I really do not like Voxcasters, myself. It's mostly because you need a minimum of 2 to make it work, the model
can is probably going to die, and IG leadership is good enough to make the failures not that likely. Additionally, it eats an upgrade slot for the command squad (which I usually fill with grenade launchers) I think Commissars, while more expensive, offer more general utility. Sisters Priests are even better, but they don't help your Ld stat at all and are somewhat wasted if you're not going into CC with the IG blob.
Additionally, you'd need to run the infantry squads as a combined squad to use Prescience/orders effectively (or a HWS, but those have their own problems). And remember that you can't blob ISes from different platoons.
If you're running around with fearless blobs (priests, etc), take the krak grenades. Being able to at least "hail Emperor" charge something with a double-handful of guardsmen is better than not. Half the point of IG is weight in #s, but if you can't hurt it at all (tanks particularly) with a lasgun or frags, the squad is deadweight.
Gah, lascannon HWS. I... can't say I don't understand why you would take them, but a 60pt lascannon with guard BS is about 45 wasted points. Even with Prescience, it just seems like "Oh, you need this to hit? MISS!" (same reason why I avoid multimelta dreadnoughts now). I feel similarly about autocannons in infantry platoons, but that's because I fscking hate having weapons like that on such a brittle model (yes, taking them in an IS reduces the brittle factor). If you want to play "platoon-sized HWT", take a single IG platoon and load it up with 4 squads instead. Or drop one of the platoons and take a pair of hydras instead (about a 10-15pt difference depending on how the platoon is configured). While they can only skyfire, Skyfire will still hit skimmers properly (and deny them Jink, knocking back the coversave a couple points), and you are free to keep hydras moving around the table if shooting at ground targets. Two in a squadron gives a bit of redundancy, and you can either hold them in reserve to avoid T1 focus-fire or do some major reshuffling, add camonetting and stick them behind the ADL for silly cover saves.
In general, when outfitting an IG platoon, you have to know in advance what they are going to be for and work with that. Keeping a static HW firebase means that you NEED to have the ADL for cover saves (all buildings are deathtraps, never enter one unless you opponent has no grenades and preferably no weaponry to crack it open).
On the Sisters side of things, I've been having better luck with smaller squads of battle sisters (6-7) than giant blobs. You get some better granularity for your Acts of Faith and the ability to take more flamer/melta in general than you would otherwise. And you get more troops units to throw around. The downside is that they're more easily shot down.
I myself tend to run very aggressively with IG, so there'll be plenty of points on which I will disagree with other people around here.
Other than "I've been Expecting you", why Coteaz? Seems a bit of a waste given that you don't really have any henchmen (Crusader/DCA/Priest mixes are rather scary).