Waldo,
In my opinion, yes, you can add too much campden. But if you stick to the 1 tablet per gallon, you should be fine. Too much would inhibit any yeast in your wine to ferment. The more you rack (and then ultimately filter), the less yeast per campden tablet you have. This equates to more campden inhibiting the yeast. At least that's how I think of it. I am sure the more experienced winemakers can offer the nitty-gritty of it, but this is how I think of it.
If a wine is not going to be sweetened, you don't necessarily have to sorbate it. I still do, because I've had some popping corks (for various reasons, I believe), and I just want to be sure that if there is any residual sugar, and if by chance I did not add enought campden, renewed fermentation will definitely not take place. Again here, I am just telling you what I think. Again, I do this just as a precautionary measure. You don't have to do it.
Hope this helps....
Martina