I am thinking of making some kpop demon hunter character designs namely Mira romance saja and jinu saja in wolf form

I just saw K-pop demon hunters! I know you have to be careful doing stuff that could be copyrighted.

I think your best bet would be to start slow and take things in order. Other's could pitch in here, but this is the general approach I would take:

1. First come up with an ideal wolf you'd want. Play around with different poses, patterns, and colors in the Demo tool and come up with a dream wolf to work towards, or decide on an existing wolf you'd want to end up with the apparel. For a highly customized CA, it's either going to be very expensive or not an option to get it on all breed/sex combinations, so you'll want to have the pose picked out in advance and the colors of the wolf will be important to make sure the CA design complements them. Something that looks vibrant and striking may look dull paired against the wrong wolf colors, or a yellow may look more green depending on the undertones of the wolf it's on.
2. Come up with a general idea of what kind of apparel you want. Since there are a lot of restrictions you need to consider to make sure it's not infringing on copyright and follows all CA rules, you'll want to have your idea fleshed out as much as possible before going to an artist. Which outfits from the movie are inspiring the CA specifically, and how could they be modified to be either more generic or more unique so they aren't a straight copy? How much coverage will the final look have, and will it need to be split into multiple apparel items or can/should it just be a single item?
3. Find an artist who is willing and able to work on the project -- to me, this could be the hardest part depending on exactly what you're looking for. Every artist has a different style, skill set, etc. And you'll want to find someone who matches your needs and timelines, has a price range you can reasonably meet, and is able to take on the project (especially if you will need multiple CAs designed to have each of the characters).
4. Once you have an idea of who could create these and how much it will cost, then would be the best time to figure out the best way to fund it. This would mean answering some questions like: do you want this CA to be exclusive to you? Available for sale after you receive your copy/copies? How much is the artist planning to/able to charge if they go on sale publicly? And then depending on the cost and the answer to some of these questions, you could figure out the best way to fund it. Especially if the artist needs $USD or alternative currencies, it could be more challenging. If they just want MS or item trades, what do you have to offer them? Can other people pre-order copies to help fund either the Custom Apparel Token or the artwork itself?

lalierre has some great advice, but I'd also add to check out the existing Custom Apparel in the store. If something you like already exists, that will save a lot of time and money! Then you can plan your wolves based on the poses available in the CA you like. Or at least it's an opinion.