1. .15 is probably a bit much. Take medium-ground, or even unground material and pack the FF bowl fairly densely, even with the top edge of the glass bowl. That will measure around .11-.13 in my experience. This is plenty, and a bigger bowl than many users like. Just fill the bowl as much as you like and see what results you get. 2. Whatever works for you. If you are getting good results with 20 second hits, you don't necessarily need to work up to 30, unless you explicitly want larger hits. Sounds like you are doing fine. 3. If your material is black (ie charred) and spent in so few 20 second hits, I am guessing you aren't putting much in the bowl. Try using more and stirring every three hits. But yes, if your material is dark brown or even black, and tasting not so great, you are pretty much at the end. The FF won't vape at high temps, and if you're getting charring you are probably extracting everything of value and then some. I keep going until I can't pull anymore vapor. Sometimes the material is darker than others...but when long button pushes and stirring won't produce more vapor, I'm done. There are things you can do with the ABV, even put it in a high temp vape to get the last bits, but for all FF purposes you are done. 4. Your battery sounds bad. 6 twenty second hits is not normal. You should be getting four times that. Call FF and get a new one. 5. Personal preference, mood, time of day, strain (obviously)...no one answer here. Sometimes I'm fine with one or two hits. Sometimes it takes ten. So many variables affect it. Get a new battery and maybe try to use more material in the bowl to prevent charring and give yourself more hits per bowl but otherwise you sound like you're off to an excellent start. Have fun, experiment, let us know how you get on.