I've never brewed with tea, but if you're doing a hotside addition, I'd be prepared to pull them out quick. I like my green tea and oolong steeped for 2-5 minutes (depending on the tea), at 180-185F. Grassiness happens quickly with green tea, but there's a lot less astringency than with black.
I do think you will get the best results with a hotside addition using green tea, but that doesn't allow you much opportunity to add to taste. This might be worth brewing a small batch to confirm time & quantity for the tea addition.