Step one: Choose the perfect color scheme (I like Behr paint from Home Depot).

For all of the walls (except the focal wall), I used "Fresh Day" in semi-gloss, and for the focal wall I used "Vintage Linen" in flat. The other colors, in the order below: "Retro Avocado", "Solar Fusion", "Spring Stream", "Dragon Fly", and "California Dreaming". Not pictured but used, is the brown: Ralph Lauren's "Crosby". These colors make me ridiculously happy.
Step 2: Create stencils:


I made two of each thing I needed: the tree shapes, the trunks, the bird (right and left facing) and the squirrel (right and left facing). I used .005mm Mylar sheets, cut down to 8.5" x 11". I traced the shapes onto the mylar, applied some adhesive, then cut them out with an exacto knife.
Step 3: tape off the wall.

I used a laser level that sticks on the wall to get the straight lines. And...I admit that I completely lucked out on the spacing. The shapes I created were just the right size that I was able to get a full 12 rows up without cutting the tops or bottoms off of the design. Total fluke. I didn't do any maths or anything.
Step 4...should read: "Apply stencil to wall and using a stencil brush, quickly and efficiently stencil shapes onto the wall for a perfect crisp image."
Ha.
Step 4 instead is...throw all of your preconceived ideas of how you're going to do this and how long it's going to take out the window.
That's right. I forgot one crucial thing in my planning...our walls are really textured. And stencils don't work on really textured walls. I found this out when I did the first set of tree shapes and the paint...bled...everywhere. Not neat and tidy and crisp at all. And being the insane perfectionist that I tend to be, I knew I couldn't continue with it unless I committed myself to making it the best I possibly could.
This is where you all are going to think me a bit crazy.
So...Step 4: Commit to painting each tree shape, each trunk, each squirrel and bird...by hand. Yup. I did. I still used my stencil, but only as an outline. I outlined the shapes in pencil on the wall, then proceeded to paint by hand, which leads to...
Step 5: Choose your tools.

These are the 5 tools I used to paint the entire wall. A number 3 round brush, a number 4 round brush, a number 8 round brush, a flat brush...and a pencil.
The final result:

So. How long did it take me all told? Well...I worked a solid 7 days...10 to 12 hours a day. But you know what? I really do think it was worth it. I enjoyed doing it. And I'm really happy that I committed to doing it as best as I could.
Of course, this does mean that we can never move. And that Emilia will have to live with us the rest of her life.
Totally worth it.