Homemade buttermilk is only bulk starter if you started with cultured cream before churning. If you started with sweet (fresh) cream, your buttermilk is just skimmed milk.
I used to make butter in the food processor all the time but could only do 1 quart at a time. Here's a tutorial I did a few years ago:http://solarfamilyfarm.com/?p=27
Since then, I've gone to churning 1+ gallon at a time in my Kitchen Aid using the whisk attachment & a splash guard. If you use the beater attachment it doesn't work very well. If my cream is too cold, it can take a long time to churn. If warm enough, it only takes 10 minutes or so. DO NOT walk away from the mixer......when that butter breaks, you'll have buttermilk all over the place! I've also refined/simplified my washing & working processes.
In the wintertime, it is important to have your cream on the warmer side (68-72) or it takes a very long time to churn. If your house is cool, leaving the cream at room temp may be too cool.
Also, the yield on butter depends on the % fat in your cream. If you are home and have no way to officially measure this, that is fine. The longer your cream sits on the milk, the thicker it will be come (i.e. the more fat). I will often skim only the thickest top cream (perhaps an inch or two) and save that for butter and use the part skim for cheesemaking. That super thick top cream is highest in fat and gives a much larger yield. If you are milking today and skimming tomorrow, your cream will not have had a lot of time to rise and therefore will not be so thick (not have as high a fat content). You will not yield as much butter with this procedure.
Does this make sense to anyone or am I rambling too much. I've been super busy and have barely had time to scan the forum, let alone this post!!