Since I did this write-up, I have moved on in my yogurt making -- I'm now making yogurt in 1-gallon batches. (Two gallons 1-2 times per week?! I stand in awe ...)
Unfortunately, the microwave just couldn't handle a 1-gallon batch -- it took forever to get up to heat, and didn't hold a very steady temperature, and in spite of my "rube goldberg" setup, it still developed a fair bit of "skin."
So now I heat the milk in a pan directly on the stove, stirring constanstly, to 180°; hold it at that temp for 30 minutes, still stirring constantly*; then cool rapidly by setting the pan in a sink filled with cold water. When it gets to 115°, I transfer the milk to a 1-gallon jar; I stir some of the milk into around 2 Tbs of yogurt (Fage 2% is my preferred starter, but I've had good results with some others) until smooth, then return it to the milk and stir it in. I put the jar in the yogurt maker and put on the jar lid. The jar fits into the "well" of the maker, but of course is way too big for the original lid from the yogurt maker to fit over it, so I cover it all with towels. I come back 12 hours later to delicious, thick yogurt. Usually there is very little twang if I use Fage; more if I use some other brands as the starter. But all of it absolutely delicious!
*Yes, it is not convenient to have to stay at the stove stirring for 40 minutes. I need to make an electric stirring device to go on the pot ... but in the meantime, I get a book and a chair, and sit by the stove, stirring as I read. Before I know it, the time is up!