For all my plants I like them potted to a height of 1/4 inch of the top. As to the size of the pot that ideally figured out with the roots exposed.

That soil looks atrocious for an Adenium.

David, why don’t you repost on the Adenium Forum if you don’t get more help here? I think Rob is trying to tell you that a faster draining potting mix is needed. Nice plant. Good luck with it.

You might have a better growth habit of the caudex if you don't lift quite so soon unless you have a lot of growth beneath the soil. Personally, I would leave it until it was almost bursting from the pot. but you could still change the soil of course.

Once the bark is exposed for long periods of time you can't re-bury it. I think the caudex will put on more size if you leave it buried. Your plant is lovely, hard to tell but is it a grafted hybrid? The rootstock should usually be vigorous.