If you want more strawberry flavor, you can add more fresh strawberries, ground freeze-dried strawberries, strawberry jam, etc. Go as strawberry crazy as you want (:
Any liquid sweetener works if you don't have or want to use maple syrup or agave. I like adding it at the end instead of with the hot tea, since it's easier to account for the strawberries' sweetness when you add it at the end.