I've finally made some progress!
After playing around with the devore paste and not getting a good result, I've scrapped that idea and will go for a different embellishment on the bodice. I also played around with gold fabric paint and a stencil, and have decided on gold feathers all over the bottom of the dress, probably graduating up the dress. I used mum's Scan N Cut to cut my own feather stencil, it worked quite well.
After some deliberation I decided not to make the bodysuit underneath. I'll still do the lace sleeves, but just join them into the dress. Instead, I'm planning to use boning in the dress to help smooth out my lumpy bits! I'll probably put the boning in each seam, stitching together the seam allowances to create the boning channels.
The sleeves will be attached at the top and sides only, letting them hang straight down. Not sure how I'll embellish them yet. I'd also like to make shoulder rolls (a-la elizabethan style) as I'm going for a mix of medieval/elizabethan style lines (and it's a costume, why shouldn't I go all out!).
The best part of not using the devore paste is that I've been able to use poly velvet rather than silk. Much cheaper, and so much easier to work with! The pile is much shorter and I've not had any issues with it shifting while sewing (except when I attempted to put the zipper in by sewing against the nap, learned my lesson). I don't even have to baste the seams. The shorter pile also works much better with the fabric paint. It's a great fabric, a heavy velvet with 4 way stretch. It's giving me a great drape and is forgiving on the fit!
I've put the dress together, side seams and shoulder seams just basted for now. I need the dress to be made up so that I can use the neckline to create the frame for my wired feather collar/ruff. Once the frame is together, I'll take the dress apart at the side/shoulder seams, then lay it out flat for stenciling the feathers on. The collar is going to be tricky - I'm following a tutorial on making an elizabethan wired ruff I found online. Feathers are going to be black painted gold (too expensive to order gold feathers!)
Here's the base dress. I've pinned the hanging sleeve to see how it looks. It ends in a point which I'm not sure I love, I might make it a different shape. I've got plenty of off cuts of fabric due to how it was cut out!