This is so admirable!
I bought the A-Z book on threadpainting...but it seems so daunting!

I don't know the A-Z book - but ... just take it slowly, and start with simple shapes. Keep going back to the pages where it shows you the layers of the stitches.
This is only my third project. It's all the same thing, once you get the basic idea.
:-)
A few posts ago a lady and I were talking about whether clare hanham's "Begininnger's Guide to Silk Painting" or Burr's "Redoute's Flowers" had the simplest introductory instructions, if the A-Z isn't working for you. I still vote for Hanham

Excellent! Did you have to rip out the original stitching on the leaf, or were you able to work above it?

I ripped it all out. I'd already down a bit of oversewing for the blending - especially on the small leaf, so it would have built up too much.

Pleased with it now.