i don't crush them at all. i just use 'em as i get 'em. i put somewhere between 1 1/2 Tbsp to 2 Tbsp in my strainer or tea press. I use a little over a cup of water for that amount, and steep the tea for about 2 1/2 minutes, maybe longer.
as for flavor, if you can tolerate honey, that's nice in the fennel tea, as is a pinch of cardamom. both take the bite out of the fennel (tone down the anise taste a bit).