Interesting thread. I love all the work put into it.
I myself have dabbled in the art of cosplaying sailor moon characters~~~
Here are some of my suggestions
The skirts from the team uniforms actually layer under most other skirts. They're also great for shortening a certain shirt. They give the effect of a back bow that looks accurate to the characters. Not only that but when you turn around it's an actual... back bow.
Team Durem Uniform is perfect for Sailor Moon and Mars.
Golden Uniform is perfect for Venus.
Team Gambino Uniform can be used for mercury and all the other blues ones lol.
Team Aekea Uniform can be used for some of them too..... kinda.
As I said before the skirts from the uniforms have a shortening effect with any shirt or dress on gaia. I personally like using this pose from
Reve Rouille or
Reve Marin.

When used with the skirts it should look like this.

From there, the angelic lace corset and any serafuku scarf should do the rest. :')
Oh and don't forget to add another skirt on top of it
My last forms of advice are pretty simple.
Spirited Gloves are great for layering under normal white gloves. They're the only ones known to do that so they're kinda pricey.

Satin Hairbow is perfect for Sailor Venus~
Dionaesil for Sailor Jupiter's hair balls...
Also
Candy Pop Dancer has a nice bow that works for Sailor Jupiter's butt bow.
Possessed Whispers +
Sainte Ciel: Agape for Sailor Uranus' hair.
Prince of the Sea has a cape pose that works for sailor moon. It also layers with the serafukus to go that extra mile. :0
The brooch from
Gambino's Golden Treasures works well to set your cosplay apart :')

Now for some tips!
Things to avoid....
I've seen some of the best Sailor Scout cosplays get ruined by the lack of nice eyes. While a lot of people have criticized me for using
SDPlus #272 Majoko Mariko , I have to say they really do help my cosplay stand out. However, there are other eyes that work well.
Anything that makes the face look bent out of shape is to be avoided.

I could make a list of that but instead I have a list of eyes I would use.
MP:
-
Sainte Ciel: Storge
-
Astra: Violet Winking Purity Eyes
-
Optimistic Eyes
-
Sheepy Gaze
-
Cupcake Gaze
-
Queenly Stare
-
SDPlus #325 Wendy
-
Astra: Green Blinking Purity Eyes
Shop Eyes:
-
Inquisitive Eyes (6,000g)
-
Chuu Eyes (650g)
-
Distracted Eyes (2,400g)
-
Kirei Eyes (900g)
That is all. Hope this helped. :')
Still nothing for Sailor Pluto's hair tho she should be avoided at all cost.