Hello Fids
As you know, taking T or E or whatever is a bit of a lottery, and you've no idea how much it may affect you and take you in your desired direction.
But that is far less relevant than how you feel about yourself. If you are sure that this is the path you need to take, then take this path and do not agonise over it. I think I'm quite a bit older that you, and I can tell you that I never regret decisions I've taken, but I have frequently enough regretted decisions I've avoided taking. If you know your mind, and feel with certainty that you wish to change gender, do it, so that you may enjoy a full life of it, compared to the half-life which I shall enjoy of it.
Yes, your family will be surprised and hurt, but these things frequently get better with time. It's hard for them to visualise you as a person of the other gender, but when you start to play that role, and when it becomes who you are, then they will find it credible. I think you also might find it good to convey to them how alien you feel in your current body - the sense of wrongness, which I am assuming you notice from the time you wake up.
It's my feeling that the key thing is to have a plan and a vision for your life and your transition, rather than just vocalise "I want to be a boy/girl" with no commentary. Create a plan, discuss it with your therapist or a good friend, share it with your family, and stick to it. I know it sounds geeky, but my therapists loved that I delivered them a roadmap of my plans, right down to approximate dates.
These first few steps to get yourself on the road with your family are hard. But persevere!
Edit: WPATH is a very sensible set of guidelines - do download it and share it!
Good luck
Julia