Oooh! This sounds interesting. Yes, this could taste very good. What size are you starting at, 1 gallon or 5? I made a saffron, sage, rosemary, and thyme mix that was divine. I was pretty conservative on my proportions for a 5 gallon batch. I used 2oz each of fresh rosemary, sage and thyme and 1/4 cup of dried saffron. (I got a really good deal on it and had a lot on hand.). I think you could put quite a bit in of each. The lemon grass could act as an acid flavor so lower the amount of acid blend accordingly (or estimate). You could use a lemon basil to enhance the lemon flavor, or if you wanted, a darker purple basil to add a small amount of color. Those flavors are not too overwhelming so you could add a lot. You could make a plain mead and a strong herbal mead and mix to taste if it is too strongly flavored. I'm looking forward to hearing about it.
(By the way, you can get lemon or purple basil from gardening centers and it is pretty easy to grow if you have a small amount of garden space or you could even grow it in a pot by a south facing window.)
Tomico