When it comes to the menstrum, I'm of the belief that you can't add "too much" IPA. The more room the alks have to migrate too, the better.
Once you strain the menstrum and add the 1g of fresh caapi leaf, I'd personally recommend allowing that to soak everything up because with a little luck, you'll have well over 1g of 10x caapi. For each gram of the 10x caapi, add 1g of spice.
As far as evaporating the IPA, it's all about surface area. Once again, with my personal preference, I like to use a shotglass when making small quantities. I'll put the 1g of fresh caapi in the shotglass and keep adding the menstrum as it soaks it up. This way I know the leaf absorbs the majority of the alks and they don't just get stuck to the evap container.
Once everything is mostly soaked up, I'll move it to a pyrex baking dish to allow for a more complete evap. I'll usually leave it in the baking dish for at least a day or two to make sure all of the IPA has evapp'd. A small fan greatly speeds up this process.
There's a ton of different ways to do it. I've just listed what works best for me. Good luck with everything!