Over the weekend I got a pattern drawn up and transferred to the fabric.
The fabric is a medium blue dupion silk, which I've backed with calico. After messing around with colours a bit, I decided I had to options. One option was to make all the embroidery pale, which would look very pretty and delicate. The other option was to use the bold colours I had originally thought, and outline everything with metallic gold. I thought this was probably the better option for the recipient (the wedding dress is red, so the flowers match).
This meant that I chose to go with a cream for the letters, rather than gold - I didn't want to use both a yellow and a metallic gold, and I don't think my goldwork skills would be up to the delicacy of the letters.
Here is the pattern - both the original tracing, and the photocopy that I played around with colouring in.
I'm using DMC stranded cotton, mostly because of convenience. I only have two weeks, and I didn't want to lose time to waiting for silks I had ordered to arrive. (I may have been able to find the right colours locally, but I didn't want to rely on it).
I'm fairly sure the gold thread I have is Kreinik japan thread, but I've had it sitting around on an old sewing thread spool for a while so I can't be sure.