I've seen a lot of people wanting to dress up as this character lately (And I don't blame them, she looks awesome!) but the hardest part about this, obviously, is all the feathers and if you're looking to make it as accurate as possible, be prepared to put lots of work and time into it because feathers, especially ones so small, in those colors, and so many are not typically easy to work with.
Looking at the reference of her, it looks like if you were to be making it, instead of making all of it one giant piece, the torso would be a separate from the arms and possibly the legs as well. The arms, as I'm imagining, would be connected to an undershirt (instead of say, just having the sleeves by themselves on your arms somehow connected to the main shirt)
I was looking at some pictures of feather shirts/dresses, and while most of them had really long/crazy feathers, I was able to find some that had smaller, neater feathers.
Also, as you have most probably noticed, Toothiana's design is based off of a hummingbird (though her feathers look a lot more ruffled/split then the usually smooth ones of a real hummingbird) And also, when I saw her design, I also thought of Peacock feathers for some reason (Not necessarily the long ones, but the smaller feathers that are on the peacock's body, so if you were willing to use real peacock feathers (Which is unknown to me how good of an idea that is, or how exactly you will come across those), you could use bits and pieces from the longer ones, or just find fake feathers that look similar to her's, a hummingbird's, or possibly a peacocks.
Here is a dress (mainly the upper part of it) that I found looked similar to hers, but again, I am not entirely sure how they did this and I'll have to keep researching about that (Pics v)
If you can't find how to make feather clothes, or afraid that it might possibly be too difficult, messy, or pricey, you could also make the feathers, instead of using real ones, out of some sort of fabric/material and again, while making the torso separate from the arms and possibly the legs, make it sort of how chain mail/scale mail is made (Also, and possibly even using some sort of lightweight shiny metal as the 'feathers"?) Pic:
I'm really not sure how to go about making chain/scale mail, or what material would be best to use in this case for this costume, but I'm very sure that there is a tutorial online on how to make mail sorts of clothing.
In the end, I'm not sure how easy it is to work with feathers (My best bet is that it's not) and they could probably be messy/pricey and like you said, bulky, unless you find a way to make it look extremely well like it did with the above pictures (with the red and with the gold dresses), then using real feathers may not look at well as it could be, but nevertheless, good luck if you do go this way
For the mail, this would probably be an easier alternative, but of course, not sure what material you would use, and you probably wouldn't be able to look like actual feathers (obviously), but you can definitely try doing scale mail and cut the "feather scales" into more of a shape like hers are in.
For the head dress... I saw someone on DeviantART do makeup very similar to hers (Which by the way, looked amazing) but I am not sure how you would go about doing this, whether it just be a sort of tiara/hat you can easily put on when you need with limited makeup, or whether it be full makeup, feathers and all, because unfortunately makeup isn't my area of expertise. That's all I can really say about this, and I wish you luck and all other Toothiana cosplayers the best of luck with this costume and I hope I was able to be of some help