Not really sure what you mean and there really is no knowing if you truly added enough or added too much sulfite without testing it. The more you add and bulk age the more you need as less gets held as free S02 each time.
Well I have been just tossing one in each time I rack. I've had a few wines come out not so good, drinkable, but not to my liking. I'm really going for complete accuracy this time. I also keep notes on everything I do.
Definitely sounds like you are over sulfiting.
I add it at the beginning, again at around 2 months and if you bottle within the next 2-3 months no need to add any more. I believe, they will correct me if I am wrong, that 3 month intervals is a good rule of thumb.
Basically at start to stun wild yeasts and let your yeast of choice do its thing. Then again when fermentation is done to protect the wine from oxidation. Then about every 3-4 months with1 tablet per gallon as always or 1/4 tsp per 5-6 gallons. If bulk aging a long time though these #'s can be very weak as less and less s02 will be kept as free S02 in the wine and that is the S02 to be more concerned about.