Hi Averil! Honestly, I wouldn't soak them 24 hours - you don't really need to soak them at all, although some do (and I have, but it's not necessary). If you leave them soaking too long they will rot quickly once in the medium.

Cactus mix / perlite is great! I would say in comparison since you're familiar with adenium seed - better draining soil than adenium seed and will take a few days longer to germinate but overall similar. Don't let them dry out but don't keep them super wet either - you know, that happy medium!

A heat mat will make them very happy, I would definitely do that if you have one. Good luck, how exciting!