In the vast majority of cases, a MTF will know if/when to start and/or stop.
A therapist can help you talk this stuff out, but it should only be your decision. There is no shame in waiting and thinking this stuff through. Transition is not a race nor is it a requirement.
If some day you start, and it feels right, you may think, "I could have started earlier!". Really though, the only right time is when you are ready.
Your desire to integrate your inner and outer self is noble. It is something many have attempted to do without HRT. I have not heard many success stories, but I don't think that is the type of story that is shared as often.
Do you have any friends or family who you can open up to about this? It seems you have your trans feelings so sequestered, you may be prone to guilt and shame if you came out to everyone at once... but to one or two close friends who you KNOW will support you no matter what? That is a great way to start the integration process.
Also an AA may be a good place to start. They are not addictive. Your fear that you may not turn back, must weigh heavily on you. You can turn back. Fact is, AA's are much more noticible than hormones early on. Within a week, you should have a good idea what life with less T is like, and there should be no permanent physical side effects at that point. It is not a decision to make lightly. There will be a window of time before you will need either T or E in your system, and your questions and concerns seem to be linked more to T than E right now. It is quite plausible you will find some answers simply by reducing the T. So, hopefully you and your therapist can look at this option.
I saw somebody else post, "You don't get less trans." in one of our forums today. That rings true to me. But it does not mean you must hurry.
Another quote I have seen here, "Once you come out, you can't go back in." seemed worth sharing with you.
Good luck,
Tori