I do bullet proof coffee (not the brand name) a recipe I found and there is nothing wrong with it. I feel great, enjoy my coffee, and at times do not feel the need to eat till lunch. This is your journey, you need to adapt it to your needs. The Keto Diet by Leanne Vogel is a great resource.
I used to do the butter but I don’t really like it. I love my coffee black. I think if you are struggling to get fat in your diet it’s a good idea but I don’t have that problem. I will occasionally make a mocha with cacao, stevia and MCT oil but it’s not daily. Maybe weekly at best.