i tend to go by broad shapes and colors than what the actual clothing items are supposed to be, half of the time i like having a general idea of what i want the cat to look like regardless of what's available and then go through what is available and try to get as close as i can.
for example, this outfit started with the general idea of "shady wizard's robe"
and for this one i just generally tried to make her look kind of like a dog... or maybe just a very ambiguous quadrupedal mammal
other than these more sweeping ideas, i try to keep an eye out for where i can add interesting bits of contrast and focal points to the outfit, for example the light blue highlights on this outfit, mostly just going off the fact that their name is lightning
or the starfruit pendant here, this outfit is generally meant to be sort of summer-y, even if starfruits are winter exclusives lol
i also like to try to use layering in interesting ways, the black feather scarf on this outfit makes it almost look like there's a more pronounced shadow under xir head
and here i've used a few pretty different pieces of clothing to create a repeating pattern of white bands
i also tend to use particles fairly sparingly as i feel like they create visual clutter when almost every cat in a village has one... but that's mostly just a personal preference, i know for a fact that isn't universal. i usually use them to add a general bit of contrast in an outfit that's looking otherwise pretty homogeneous.
i hope any of this is helpful? i have some pretty specific tastes and i like when outfits get kind of out there more often than not, a lot of the outfits i've made that feel a bit more mediocre to me are probably the ones that are more traditionally good looking.
in terms of money- i get most of my money from clothing, funnily enough. i sell on the open market once a week (when i'm more active, there were a few months there where i wasn't selling anything) and build up cash. but also i play at a relatively slow pace, so that may be a bit slow for you. if you're worried about selling anything you need, i'd stick to selling any duplicates you have, and make sure to plan out outfits beforehand (or be fine with missing a few pieces before you can finish it off)
good luck! outfits are one of my favorite parts of this game, hope you have fun dressing up your kitties :)