The standard for making most herbal teas is 1 teaspoon of herb, in this case chamomile flowers for every 8 ounces of water.
When you are using a french press, the flavor will be stronger so you may want to try just a bit less of the chamomile to start.
A nice touch for what you are doing in a four cup french press would be 3 teaspoons of chamomile and 1 teaspoon of lavender. This makes a dreamy tea! Great as a relaxing tea and a stress reducing tea.
To sweeten, use honey and a touch of lemon is always nice.