Don't worry too much about the exact temperature. Any temperature you can obtain with the water bath will be fine. The water bath tops out at the boiling temperature of water, so it will not allow the temperature to get hot enough to ruin anything. But even if the temperature is a bit lower than the 220 you mentioned, I think giving it an hour should be enough time to decarb it. Just keep a good gentle boil going in the water bath and let it go for about an hour.

I would think the coconut oil should work fine. This is kind of an odd recipe, but I wanted to include both some kind of fat (or oil) and some alcohol so that you would have both of the materials that can disolve and transport THC. Might taste kind of wierd though.

Let us know how it works out!