Does anyone have recommendations for dosages for Vitamin B12, Vitamin C, and magnesium that I should take in order to receive maximum benefit, but not overdose?

I am new to all this alternative stuff, but I am at a point where I am willing to try anything to alleviate my symptoms and traditional medicine hasn't come up with much so far.

I just bought the stuff at the grocery store. Is that what I should be doing or are there better places to pick up supplements? I am just taking the recommended dosage. I figured this was as good a place to start as any.

I am trying to relieve these internal tremors that I have had since May. I also have an incredible sensitivity to sudden and abrupt changes in sound. My left arm feels weak (but I have strength, it just feels "awkward" to move) and I have pinpoint pain in my left arm muscles and back under shoulder blade(always in the same places). These are the symptoms I am trying to alleviate. Are there any other suggestions for what I should be taking?

I also have insomnia when I am off the medication I am currently taking for the tremors (60mg/day of propranolol).