Very interesting indeed, but I'm not sure how much I can help...
For the current idea I suggest an ECL of +7, for higher level games, I think the general consensus was that a full half celestial with wings was about ECL +3 and one without was only +2, while a Divine Rank 0 (no Salient Abilities) was +4. Not to mention +7 (+1 Aasimar with +2 Wingless Half-Celestial with +4 DR 0) seems the perfect number for ascending into celestially divine status (as I think you mentioned part of your campaign has drawn from similar sources). This doesn't include any HD or class skills, but a "monster class" would probably work too. Take into account that SR 32 isn't that big at ECL 27, (A drow would have SR 36) and it doesn't scale like a drow's does.
Alternatively, WotC has recently put up the
'Celestial Paragon' on their website, which you might want to use as a basis for a full-blown PrC if you decide to go that route (For the second transcension ability, WotC suggests to add on the Celestial template)*. I say basis since the PrC over all is generally weaker than a normal one, especially compared to the Void Initiate right below it.
*Precedence-In the Fiend Folio-I believe, there's an outsider race that has the Alienist as a common class for their race, so they ruled that at level 10, since they're already outsiders, that they simply gain the pseudonatural (T&B version, of course) template.
Consider the level progression of a Chosen of XX deity template, ala Forgotten Realms? I have a basic template for it which I can find if you want it (it may not be on this comp though, in that case I got it from Kalanyr, who's also a Wyre addict

)
Anyways, I hope this post can work as thanks for your help with my Primeval template
Edit-Btw, I saw Shomei at the Rogue's Gallery, very very nice. If you don't mind me suggesting, a variety of PrCs would fit her very well.
-The Summoner PrC from Relics and Rituals I, requires that the summoner makes a pact with an entity (such as a devil lord or similar), and allows the summoner to choose from the next higher list when casting a Summon Monster spell, with Summon Monster 9 either summoning 1d4+1 8th list critters, 1d3 9th list critters, or even the Summoner's master...It also has some metamagic feats
-The
Nar Demonbinder from Unapproachable East, which has been posted on WotC's website as well, I suggest not using the alternate spell list though-that's just clunky and nuts (not to mention, incomplete -but its easy to infer the abilities of the class onto a 10 level progression). Instead, I suggest splitting out a +7 bonus spellcaster level progression. This PrC has all kinds of fun abilities, and if you read the wording, its not specific to Demons, so you could just rename it the Fiendbinder or Devilbinder. If you do make it specific to Evil outsiders, maybe you could boost up the spellcasting level progression (if you take my suggestion).
Anyways, sorry to babble on, Shomei is a very interesting character though
