If you're using a Nutribullet or a similar small blender, there is no need to preheat the blender. If you're using a normal large blender, I like to preheat it by putting hot water in it. Otherwise, your coffee is going to come out less than hot.
I normally use regular MCT oil, but if I am really going to need to focus, I use Brain Octane oil, which has a higher level of C8 fats.
If this is your first time having butter coffee, you may want to start with a half glass to see how your stomach handles it. If you normally don't eat a lot of fat, you may want to ease your stomach into it.
Under no circumstance should you make the coffee without blending it. If you do not blend the coffee and emulsify it, it can cause stomach cramps.