The health benefits of tea? too much caffiene?

Herbal "tea" often/usually isn't tea (typically it's made from other plants, although there are blends of true tea--camellia sinensis--and other plants sold, and I suppose some people might call them herbal teas, but that seems to me likely to confuse people looking for either a true tea or a non-tea product).

As for health benefits, it depends on which health benefits you mean. If you mean antioxidants, even herbal teas are probably going to have antioxidants, since they are plant products, but people are usually talking about true teas when they talk about this. The antioxidant properties are greater in green tea, which involves minimal heating of the tea leaves before packaging, than in black tea, which is dried, fermented, and heated much more than green tea before packaging.

I've also heard there are studies showing that adding milk to your tea somehow interferes with the antioxidant properties, but I haven't ever looked at the studies myself, because I just don't care. Drink the tea you like, the way that you like it, and make any added calories from dairy, sweetener, or whatever fit into your calorie goal. If you're eating a well-balanced diet with plenty of varied plant foods, you're likely getting lots of antioxidants and phytonutrients. I don't think it's worth stressing out over individual dietary choices (as opposed to an overall balance and variety).

As for caffeine, a cup of real (not herbal, not decaffeinated) tea on average is going to have roughly half the calories of a cup of real (not decaffeinated) coffee. If you're not nervous, jittery, on edge, or having trouble sleeping, or getting headaches when you happen to skip your usual "dose," I wouldn't worry about it.