I've not personally extracted coffee
(don't care for it as a vape flavor) but others have and reported great results. In every case they used ground coffee. My opinion is that regular ground coffee meant for a drip coffee maker would work fine but a finer grind might be better as long as you adequately filter the finished extract. If it were me I wouldn't mix coffee in with tobacco for extraction since you don't know how strong either flavor will turn out. I'd extract the tobacco and coffee separately so that you'll have control over flavor strengths when mixing. You should be able to extract coffee using the same methods developed for tobacco
(hot or cold). I would recommend using the heat assisted method at first just for the sake of obtaining quicker results. Just like tobacco, I doubt the coffee you enjoy drinking will be the coffee best suited for extraction/vaping
. I'd experiment with a full flavored "robust" coffee that's well roasted. Just my ten cents. Let us know how it turns out