Degrafting 5/6cm copiapoa questions

[Turtlehams]

Hello any tips on degrafting copiapoa? I think they are big enough and my plan is to remove all the rootstock, soak for a few mins in a fungicide, place on rack to dry/callous (maybe dust wounds with rooting powder? Maybe not?) for 2/3 weeks (another of my questions is how long to dry) then place on a pumice/akadama mix and hope they root. Such beautiful plants I want to make sure I do anything to increase the odds. I also don’t know what root stock. These are Chinese eBay plants so it’s not like I spend 1000$ on these so hopes to learn with these and then to start grafting my own seedlings. Thanks for the help!
Ham