Dale,
When my supply was in the 10-12 oz range, I was thinking the same questions as you are and kind of figured that what I would probably do is use the lactaid to 'fill out' my supply-- ie, if my baby needed 17 oz per day for her weight and I was making 12 oz, then I would offer 4-5 oz a day in the lactaid, probably mostly in the evening when my supply was lowest-- and then just watch my baby to see how she did.

I'm an RN and I counseled my new moms to count two things in the first week or so-- diapers and feedings
1.) Diapers--babies should have at least 5-6 wet diapers a day and at least a couple messy ones. They may have less than that in the first couple days of life, but by the third day they should have pooped enough to have gotten rid of the black meconium poop, and the poops should be looking more of a gold color.
2.) Feedings--at least 10 feedings in 24 hours is the goal for babies under 1 month or so. Sometimes new moms will think they have a really great baby because he is sleeping a LOT, but they don't realize that in the first few days some babies are TOO sleepy and may actually need to be wakened to feed.

I could see that it would be a good idea not to use the supplementer TOO much, because you want the baby to be eager at the breast and stimulate you to make more milk. But it would be horrid to not feed the baby enough and get seriously dehydrated and/or jaundiced. I think that weighing the baby at least once or twice a week in the first few weeks would be a really good idea while getting nursing established.

Hope that helps a little....good luck!!