Wow, I admire you committment and dedication to this! (As I know I could never be bothered)
As a fellow mother who did not particularly enjoy BFing and had varying degrees of success with DSs 1-3 here is what popped into my little mind when reading your post:
I am not sure how much a couple of fluid oz of breast milk would provide in terms of antibody protection. I know the statistics and the fact that BF babies are less prone to infection however how well it works for an individual child is of course impossible to predict. I know many fully BF children who seem to catch everything and fully FF kids who seem to have the constitution of an ox.
You are cleaning everything? I really would not go overboard with that, not in your own home. Nursery/playgroup toys should of course be cleaned regularly.
The under 5s are the group of children mostlikely to catch lots of bugs and have many, many colds and stomach upsets. This is what builds their immunity and helps mature it. And again, some of it is constitutional: some kids catch everything, others seem to never be ill.
I have 3 boys, one is never ill, one is always ill, jury is still out on DS3 (he is 18/12).
I think what you are trying to do is amazing and truly admirable. I hope it will not be too stressful/exhausting for you and really hope you will have the desired result. Sorry, I was not terribly positive... I have no experience in relactation and wish you all the success in the world. Hopefully somebody with more specialist knowledge will be along soon.