I do not know the answer to that question for myself, because I always lower the dose when I get the result I am seeking, which is to feel better. The answer to your question, "How much is too much?" is "It probably depends on the individual!" I have a girlfriend who can wipe out a herpes attack with ten drops of my CS. Herpes is her only chronic issue. Ten drops won't do it for me. But I've got a whole lot going on in my body.
I have a friend who claims he started seeing blue from taking one dose of the store bought kind. I kind of think he was just paranoid, but I didn't tell him that. Sometimes when I drink a whole lot of it, I can taste a little bit of a bitter flavor. If it tastes bitter, I would stop or water it down some with tea and sip it slowly over a couple of days. I am not sure if others can taste the bitter flavor like I can. It is probably easier to listen to your body and take as much as you need than figure out how much is too much. How sick are you? How long have you been sick? Are you co-infected? I would say don't waste any of it. If you are not feeling bad, and you don't think you need it, why take it?
I have read that some people, like the blue guy who went on Oprah, was drinking daily for years as preventive medicine. I would not recommend doing that unless you have some kind of chronic illness that requires it. I have to take it as preventive medicine, because I have hep C, herpes, and a chronic (herpes zoster?) virus in my spine that makes my back ache. If I did not have any of that, the only time I would be taking it is at the very first sign of a flu or cold or sore throat. And then I would mega dose and drink a cup a day for several days. If it started coming back, I would mega dose for another week.
The main reason it doesn't work, when it doesn't work, in my humble opinion, is because people are afraid of taking enough to make a difference. But how much you need to take, I suspect, depends on how badly your immune system is compromised and how high your viral load and/or bacterial load count is. I know that I would have to spend thousands of dollars per month to buy enough from the store to keep my chronic illnesses in check. But I can make several gallons of it for under $15. I spend $12 for new batteries every time I make a batch. It isn't really necessary, but I just like making it with new batteries. And I already have two silver bars that will likely last for the rest of my life.
Essentially , I would say that taking any more than you need to feel great again, is taking too much. Someone once told me he drank a pint per day for six months without experiencing any problems. After that he thought he might be turning a little bit blue, so he stopped taking it, and he thought the blue sheen went away. But who knows how strong it was? His testimonial is what gave me the courage to drink a cup of it. After about a cup, it starts to taste a little bitter to me, so I didn't want to drink any more. I he weighs twice as much as me.
I have lowered the dose to about an ounce or two per day. I pour a little in my morning tea and sip till it's gone. In the afternoon, I will make another batch and do the same thing. If I am getting the flu or a cold, I take it straight. I also rinse my mouth with it and gargle if I have a sore throat. But I don't do that daily unless I need to.