This is a very interesting class in concept, but a few things do jump out at me with regards to it.
First and foremost, it is a frighteningly good dip for any sort of melee-oriented evoker. A champion taking a level in this loses nothing more than a single evoker level (something Practiced Evoker is capable of fixing if it is of great concern), an in exchange gains a significant boost to Will and Fort, a typeless AC pump, a free and always-active upgraded version of an existing costume element, and free rerolls on every fort save you will ever make. Rerolls are strong on their own, and here they come as one component of a very strong framework. You mention a weak reflex balancing that out, but Champion (again, the most obvious entry point), is a Good-reflex class, and the high Max Dex Bonus on costumes make a solid dexterity score advantageous for many evokers. Barring a very brick-like build, reflex will be middling at worst.
Compounding this is that you have essentially no prerequisites - literally any chump evoker can just walk in and take 1st level with no effort on her part whatsoever. Given the thematics of the class, at bare minimum I'd require Concentration ranks, Diehard, and possibly the evoker's choice of a feat from the Iron Will/Great Fortitude/Lightning Reflexes set.
I also find the Lawful pre-req rather distasteful, particularly given how well the unbreakable, unstoppable warrior archetype fits with the most popular examples of chaos. File off the serial numbers, and I'd call this class a sterling example of everything that a Barbarian stands for - brawn, toughness, and a refusal to be bowed by any force. While the fluff says 'ascetic', the class itself is fun and flexible and there isn't really any reason to bar entry if someone wants to bar entry to someone who wants to play it more in accordance with their own story. The valkyrie, as-written, emphasizes the discipline needed to meld their differing paths together, but nothing mechanically requires the player to do that if they don't feel like it.
Honestly though, that is just a fluff quibble, as I'd hope most DMs would just waive alignment requirements as the silliness they are. My main issue is that monster of a 1st level - if you just moved some of that stuff deeper into the class and put some modest prequisites on entry, it'd be much less of a "Why not?" selection and more a choice for those wishing to dedicate themselves to being truly durable.
...eeehehehe, actually, those two are the ones in the right here. The [Shape] tags are a relic from the previous Illumination crafting system, before Shape Components were their own category.
That is a much more elegant wording. Adopted, and many thanks.
That is a bit of an oversight, I admit. Bombs have been tweaked to clarify the lack of multiplying damage. However, creatures surrounded by explosions do now face a much more difficult saving throw (bordering on impossible if they are completely surrounded), preserving the choice of "Stay still and eat the explosions, or run for it and handle a much more manageable blast?".
Thanks for pointing these out - they were oversights, mostly, though the concentration ranks one was a legitimate typo.
As for the Stargazer being able to sneak in with fewer levels on a late entry, yes, that is intentional. As much as the 'obvious' way in is Champion/Crusader, there are actually quite a few ways into the Valkyrie, and I like to think that most of them have their own merits. Fast-tracking your evoker pre-reqs with Stargazer will obviously result in weaker illumination capabilities by the end of your build, but it's a solid option if you're looking to focus as a martial adept who only dabbles in the channeling of light.