Thank you for such a glowing review! I was actually contemplating for a long time whether I should put Smut tag or not for my story. In the end I've decided that Adult+R-18+Warning should be sufficient for the new readers.
And the decision was for that exact reason - these scenes also drive the plot. Some of that is obvious and immediate, while some parts of these scenes only hint at the future events.
I'm honestly just as new and currently only a consumer rather than a creator. R-18 works and a small warning in the authors not at the beginning. If someone still complains they're doing so to be an ass.
I've replaced "fantasy world" with "threesome" as it was the only one that kinda fits out of the provided tags (and the fantasy world isn't as relevant with the fantasy genre). Hopefully, all these tags and a small quip in the summary would be enough.
I am posting every other day until I run out, so at least two more weeks. After that ill start to post with the actual speed of writing, which is closer to once a week. The entire book is fully mapped out and the plot is set until the end so you will definitely see it finish this year.