Indie dev here who was been working solo on games for the last 3 years (nights and weekends) using the resources you're describing. You can get a lot of mileage out of those assets for not much money, but it takes a huge amount of time and skill to turn them into something consistent and usable. You can usually find art similar to what you want, but almost never: - in the correct aesthetic - the right size - with the proper animations
It's a full-time job to find this art in the first place, to resize, to animate, to recolor, and apply effects to the art to help it match your desired aesthetic. And then it still is never good enough.
There's a lot to be said for having someone produce art to your requests in a consistent style, even if the quality of the art is not extremely high.