Hi Riley.
I had to make a similar career choice, except that mine was in professional dance (I'm now retired). I had a masculine body that was good for dance (one of my main assets in that world), so transitioning wasn't really an option if I wanted to continue down that career path. Well, there are dance troupes that I could have joined that would have allowed me to make a political statement while participating in something that I loved. But at that stage I wasn't aware of the significance of my gender identity and nor did I have the sophistication to make such decisions.
In your case, you could transition and still try for a singing career, but as your voice would change, it would certainly alter (most likely reduce) your chances of being successful. This isn't to say you wouldn't be successful, but at this point you at least know your voice is good and that you may have a good shot at a singing career. So, if I were you, I would take a shot at your singing career first. You could give singing a go for, say, 3-years and if it doesn't work out you could still transition. In my opinion, you have to do it in this order, as sacrificing a few years of transition time is OK, but sacrificing your voice will likely mean you won't have the same chance at a successful singing career that you currently do. Does this make sense?
I do of course realise that gender issues never leave and I have often had moments where I've seriously thought about transition. But despite this, I had a fantastic dance career that I enjoyed immensely and, given the chance, I'd do it all over again in a heartbeat. In my opinion, an artistic career that you feel truly passionate for is far more interesting and rewarding than the pursuit of a gender change. But that's just me. Mind you, I haven't transitioned, so I can't offer you that comparison, it's just what my intuition tells me. Ultimately, personal insight is really the only measure that I, we, have available to us.