Hello hello
So some general ideas :>
As for layering, I can help at any point after you buy some gear! For example I layered Amelie, Buffy, and Muffin very specifically. It's a bit tedious, but doable.
WP Gear & Decor
-Raven feathers *or* blue jay feathers. Blue because colour scheme, Raven because of colours + fascinating mythology lore (technically more crows, but we don't have crow feathers). For example The Morrigan from Celtic mythology had connections to fate, war, and death, and is sometimes depicted as a crow(or raven).
-Possibly wings - however I'm not the biggest fan of wings since I feel they can obscure pelts a bit much.
-I think Dead Eye is just a fun item in general.
FMC/Moon flower decor
-Any spirit animals, of course. I'd be a bit partial to the pups considering he's a stud, but thinking again they may be a bit morbid ToT
-The Moonflower border may be nice for him.
-Constellations, because he currently has that nighttime background. I'd go for a water sign specifically, perhaps Pisces? Two fish, in some references it's like yin and yang and often has strong associations with the moon.
Bidoo Bone Shop
-Maybe albino or Mela pups, because it's sweet ;^; but not high priority.
-White rose border. The white would be a startling contrast to his pelt, and white roses can symbolism a variety of things from peace, to purity, to youth, etc. (I don't suggest getting too many borders though, as the "thick" borders with lots of coverage don't always overlap well)
-The Crescent Moon Earring may be a nice touch.
Custom Gear
I'm a die hard fan of OCCULTIST's gear *^*
-His celestial set specifically, especially the antlers, are some of my favourites and fit the theme very well. The wings obscure the pelt a bit from what I can tell though.
If you'd rather go a gold theme than silver, the Eclipsed Antlers would be stunning.
-Moonlit has some stunning halos! They come in blue, purple and multi colour I believe. They are three apples though, but maybe if you worked it out with someone they'd buy the gear with apples and you could transfer them mush since I know you're saving for talents.
-Celestial Rings by Drakaina. They're a lovely set of golden rings that appear around the head, and I believe maybe torso, or your wolf.
-Dragonfly Wings by Rosselant. I know it seems an odd choice, but the iridescent shine on them is so lovely. Plus dragonflies live near water.
-Wisp Lantern. I actually accidentally bought two of these lol, so if the item interests you I'd happily gift it. 🩷 I find them quite pretty, and they'd fit Moonbeam's vibe quite well.
-Silver Face Piercings by Sekizen. They're just a lovely fone detail, and would show again Moonbeam's dark fur quite well.
Summer 
Night Weather: 
Clear Moon: 
