K.W.
hi,
i do not make yogurt from breast milk, but from cows milk, and i believe it will not be any different and seems like a great idea if you feel like expressing milk.
a few thoughts:
1. you do not need a yogurt maker. you can warm your jars (pint mason jars or smaller work great, no larger than a pint) either by filling a cooler with your hottest tap water and replenishing the water when it cools, or by placing the jars in the oven (with the lid off), preheating the oven for a couple minutes, turn it off, and several hours later repeat the process. both these manners take between 12 and 24 hours.
2. i would recommend against using a freeze-dried yogurt starter. the cost of these is more expensive than just mixing in a dollop of yogurt with live, active cultures (such as stonyfield organic, or dannon). you can then use the yogurt you made as the starter and repeat the process for several weeks until too many other bacterias get in and you buy a yogurt from the store again.
3. the yogurt will most likely be a little runnier than that from the store. smaller containers help for more solid yogurt, but most store yogurt has pectin added to it. probably though you aren't so worried about consistency and are more interested in the cultures!
4. using homemade yogurt is great also in breads (a good way to get protein into bread, crackers, etc). i believe that both the mennonite "more with less" cookbook has information breastmilk compared to other lactic sources, as well as the "king arthur flour co. cookbook".
i have been making yogurt and cheese now for quite some time and if i can be of any other help feel free to contact me.