Wow
@Tracy von Elling that's a really big compliment! Thanks
I used a wood carving knive (but I think clay sculpting tools will also work, maybe even better) and filled the cutouts with fresh soap at emulsion. I think I had to use a chopstick to get the soap everywhere. Anyway, I remember not having to be very precise when filling the soap cutouts. I just poured it in and wiped any overflow off. The soap batter also had enough surface tension to stay in place on the edges.
I planed the soap before carving and filling and beveled afterwards. The details were too intricate to make deep cutouts. However, I did feel that deeper cutouts made it easier to fill.
Also, I used stencils for this that I made by looking up pictures and tracing over them with see through paper, then cutting through the paper.
Hope this helps!!