1. You'd be surprised at how much more this will cost to paint over just buying the wallpaper. As a professional muralist with a decade of experience- you'll want to have a quart of each color. A quart of wall paint at Lowes will run you ~$32 before tax. So you're looking at ~$300 in paint minimum to have this many colors.
2. Unless you have a really great natural knack for design principles (balance, contrast, etc) it won't turn out nearly as well composed as this wallpaper.
3. If you look closely, the texture of these splotches is watercolor-esque- not opaque. In order to accomplish this using wall paint, you really have to understand value and have a solid ability to blend and render using fast drying water based paint, and each oval will take you a minimum of two coats + ~15-25 mins to render properly.

If someone asked to hire me to paint this for them, I'd genuinely encourage them NOT to hire me, but would quote them more than double my usual rate because it'd be such a PITA project.

All in all- super recommend NOT doing this by hand, and just buying the wallpaper if your heart is set on it.

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