Great concept. Been thinking about variants thereof for a while now, so I'll stop lurking moar and actually start posting. 
Imo, the real strength here is less the BIG once-per day Fragment of the Song Nova, but the effortless, ressource-unintensive "mini-nova" a Chanter can put out pretty much every encounter. So I feel the Encounter Nova is the more interesting aspect to optimize here.
Some questions before I go into some of my thoughts on that:
- You say your setup phase stuff lasts all encounter. Battle Chant in particular doesn't, though?
- Luminary Ring is probably one of the most vaguely worded items in the game. The kinds of powers it affects generally are not "ranged", but bursts and such. As such the term "range" in its description cannot be a precise game mechanical term, but must be a "normal language" word, for "whatever distance measurement the power uses". Thus it should by all standards affect "adjacent" "ranges" and increase them. This would greatly benefit the usability your Magic Weapon at-will there to get your backline buffed with it too.
That done, some thoughts and Ideas about improving Encounter Nova powah:
- Our driving goal should be to get Inspire by Example out pretty much every encounter. Thus we need an action point generation infrastructure, for which we need or at least could use outside help. Cleric MC is taken early, so we can use Symbols of Victory right when we start needing them, which is good. A good portion of our DIUs should probably be earmarked for these. We still need crits to get those delicious AP though. In Paragon, Divine Oracle teammate would be ideal here to toss us an autocrit in the mop-up phase of the encounter, failing that we can try to rely on natural crits (underlevelled Jagged Weapon?) and/or rationing IBE (boo!) when the encounter is weak enough. In Epic, there are more options for team help (Action grant, Legendary General) of which *something* might well be present, so this is largely a Paragon playability issue. (Actually, Legendary General is great for the Fragment Nova anyway. This guy really really wants Boulder as his tank :D)
- In epic, a solid addition to our ressource cheap Nova would be Adjure the Chosen, I think. Cleric U22 Encounter Power, Standard action, group+self get +2 power bonus to attack, damage, speed, and 18-20 crit range ENT. Standard action non-attack buffs hurt, but this is a strong enough one to justify the cost imo. We're already cleric MC anyway, and don't even have to lose the excellent Severe the Source for it, since thats an attack power (despite also not actually attacking). Overlaps with the hit buff from Battle Chant, we can just leave that for later in the encounter. We'd also lose Climactic Chord, but thats a daily anyway, which I'm biased against in this list. :P
- We have one (or more, if we include Adjure) Cleric encounter powers, and any serious (ideally any period, AP infrastructure permitting) encounter has us spend an AP. Divine Mastery to get that power back for another turn of buffage after the first seems worth consideration.
- No mention of the absurdly strong value as a BUFF that Majestic Word gets for a Fatesinger. Fate's Clarity gives the targets (2 due to Supreme Majesty) the rerolls even if they spend no surge for the Word, so they can get buffed without wasting long-term/daily ressources, ie surges. (Some heal capacity *in this encounter only* is wasted, sure, but that's worth it to maul the encounter to near-triviality in the opening gambit, sufficiently less healing is probably going to be required to make up for it). This reroll with Adjure from above gives 2 people Avenger-like critfishing in the Nova turn (accuracy too, but IBE should cover the autohit)
- Quickened Spellcasting could allow us to add one of our buff at-wills to the 2 non-attack-buff standard actions. That has to hit though, and we're already at 2-3 strong hit-independent effects, so adding hit dependency would be a style fail. I'm not convinced. Incidentally, since with Adjure we don't need to hit anymore for vital effects and would habitually spend our AP on a non-attack, we could kick Action Surge after Paragon.
- For a casual nova, we obviously don't want to spend 2 AP, getting one to spend each encounter is nontrivial enough. We can still use our second AP use from the lvl 16 feature though, by wagering it to give someone another Action during the buff via Destiny Fulfilled. That's gonna be pretty much auto-hit, so we'll get it back. For real lulz, have this be another big hit independent buff of theirs to improve the Nova if available. (Relentless Assault would be awesome with the groupwide critfishing I'm suggesting here, but getting that often enough to count as semi-casual nova requires rather specific build, I want to keep constraints on other groupmember builds to a minimum, ie nothing beyond "GIEF AP OR NO BUFF FOR U")
- Boots of Eagerness should be kept in mind here if we dig up another minor action buff (like Quickened magic Weapon), but for now the regular alotment+AP is enough: move in position if needed, standard Adjure, AP standard Sever, minor Majestic Word.
- This was a whole lot of ideas about encounter novaing, but the daily fragment nova DOES get improved by this too. For one, we can do this in the fragment encounter too (and just add some dailies to taste with the bonus actions), improving it alot. More importantly, the encounter Nova is brutal enough that everyone except us should rarely need APs in normal encounters, so saving enough AP for everyone to have however much they can spend on the Big One should be trivial.
