maybe "too much " is more like "יותר מדי", but "too many" is more like "הרבה מדי" יותר מדי is more universal, I think.

If you are taking about amount you can use both. But if you want to say: it's a bit much or you are bothered of something or someone and you are going to say something like: I've had it with someone or something, you should say :זה יותר מדי