The joke that I often like to use is:
Sure just Effect/Stylize/Awesome Fill Pattern.
It's right between Awesome Billboard and Awesome Vehicle Wrap.
In those examples, it looks like all of the elements were carefully placed.
Another approach might be to start by creating clipping masks for the primary forms - the house, the shoe, etc.
Then taking your various fill components, the flowers and whatever, and creating scatter brushes. Edit the settings, whatever.
Then use your primary forms as clipping masks.
You would likely still have to manually place some elements, and the clipping masks would likely hide parts of some of the brushes, soyou'd have to play around with it a bit.
Illustrator has a ton of built-in symbols and patterns that you might find useful. Although, I used to operate under the idea that I had to create everything from scratch, everyone gets custom work.
I don't operate that way anymore. If I can buy a vector for $6 or $120, and it's pretty close to what I need, I buy it.
So, you might draw all of the fill components, or maybe buy a vector pack that has components that you like.
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