Out of curiosity, is most of your exposure to people doing voice training for trans folks online?
My default assumption would be most providers are cis, but I have approximately zero exposure to online voice resources and my limited exposure to IRL professionals has been entirely cis people. (A quick google does not tell me whether the authors of The Voice Book for Trans and Non-Binary People are cis, which seems to be the "modern" book rec.)
It's true that I'm only familiar with two country's legal systems (and both are common law jurisdictions), but as I understand it, your "legal gender" in the UK is only well-defined if you acquire a GRC, which is something only trans people do, and plain old doesn't exist in the US. (To be fair, I imagine if you brought a discrimination case on the basis of gender in the UK your gender might be established as a result, but among the long list of things I am not is an attorney (anywhere, never mind in one of the UK's multiple legal systems).)
Amusing, the letter that comes with the GRC asserts that it should suffice to establish your gender for any interested entities, which is decidedly false overseas.
Both "biological sex" and "legal gender" are considerably more nebulous than you're assuming.
Let's say you define "biological sex" by genotype, seems unambiguous enough, right? It's a pretty good bet someone is 46,XX or 46,XY based on sex assigned at birth, but generally people don't actually know for sure.
Likewise, in many jurisdictions, you don't have a legal gender, you have a collection of gender markers. Ironically, trans people are often the only people who actually have an explicit declaration of their gender by a court or other legal mechanism. For cis people, the fact that it's a fractured mess generally doesn't matter.
VisualStudio is different from VSCode.
I'm not just referring to the, uh, directional aspects of medical transition, though, but gendered experiences more broadly. For example, when I was in junior high, a social worker at school taught me to put on makeup. The WTFness of that is something that I'm going to want to discuss primarily with people who were perceived as gender non-conforming girls as teenagers [edit: including those who grew up to be women]. Being afab is not a requirement for that experience, but people with that experience or similar are going to be overwhelmingly afab. I get something different from talking about gender with trans people with experiences that are substantially different to mine (both people with different genders to mine, people with different experiences of gender pre-transition even if their actual genders aren't all that different). I'm not saying that people aren't prone to overgeneralization (there sure as hell are a lot of people out there acting like all non-binary people have genders that might be described as adjacent to "woman"), nor that gender assigned at birth isn't something that people aren't prone to overgeneralizing about, but your claim that it's wholly irrelevant is preposterous.
If you want to make your assigned sex at birth a part of who you are, I won’t stop you, but to me, I’m not comfortable doing it. Being comfortable with your assigned sex is literally just what being cis is, and I’m not even remotely cis.
You realise this is saying "Well I guess I'm more trans than you"?
Please don't. If there's some of particular interest, link to it with some commentary.
I think you're dismissing their point too readily. It's true that there's nothing I share with every other afab person on the planet other than a box that got ticked by looking at our genitals when we were born, but if I'm looking for someone who shares a particular gendered experience, my best bet is probably another transmasculine person, particularly one who transitioned at a similar age. It's reductionist and transphobic to argue that one's socialisation is determined by gender assigned at birth, but it's also reductionist to pretend it's irrelevant.
What does stealth mean for you? What aspects have you worrying that it'll result in isolation?
I'll be honest, I have a bias here -- I do find being in situations where I feel I can't talk about being trans isolating and find/found stealth (or even the state of "waiting to make up my mind") fairly unhealthy. But my definition of stealth is something like "willing to take steps to ensure others do not find out one is trans even in scenarios where safety isn't a consideration". I probably fit some people's working definitions of stealth, though -- I generally tell people I'm trans in two scenarios: it's immediately relevant or I feel like our relationship has become close enough that I would like them to know. That has been how things have evolved naturally as I've gotten further from the "active" phase of transition and moved around the country. I actively talk about being trans at work (okay, that's maybe no one's definition of stealth), but only in diversity-focused contexts, so do my immediate coworkers know I'm trans? Nope, they don't show up to that stuff. I personally value having trans friends/community, but if that's not important to you, you're not obligated to seek out trans people in a new place (and, honestly, a lot of trans spaces are very transition-focused by necessity, so finding community can be hard if you're in a more steady-state transition-wise).
On the top surgery front, I have a friend group who figured out I was trans after, oh, a decade of knowing me. My entire medical transition, including top surgery, took place in front of their faces. I met them at a time where it was a tossup how people read my gender and it was more important to me then that they read me as a guy than that I be out, and then a decade went by and I'd became close to them (i.e. at least some entered the category of "people I actively want to know I'm trans") and it was like "So, uh, funny story..."
tl;dr Moving as an adult is kind of isolating by definition and you have to rebuild community. If you don't seek out trans community as part of that rebuilding, odds are you'll end up as stealth as you want.
The library assistant (not even a trained librarian) had such a huge impact on the culture of my high school. He wasn't particularly well-liked, as he was the rule enforcer (no playing Flash games on the computers during lunch -- I think you could play before school), but he'd put a stack of photocopied NYT crosswords out on his desk at the entrance to the library every morning and so many kids did the crossword.
It's not just steering kids to books like the quoted parent said; at the schools I went to, it was often non-teaching staff who you felt were looking out for you as an individual, often because you interacted with them mostly one-on-one. Certainly, there were teachers who played a huge role in my life, but I will remember the name of the custodian at my primary school for far longer than I'll remember the names of some classroom teachers. (I already don't remember the name of my 2nd or 5th grade teachers, now that I'm thinking about it.) The library is basically the only place you can stash a kid "to do an independent study" (aka let the smart kid amuse themselves), or take a make up test, or hang out when the school elevator is busted and they can't get upstairs. I guess you can use a "disciplinary center", but let's be real.
I ended up with like half an autism diagnosis a bit over ten years ago. (Basically, I saw someone for other reasons and they said "Um... I'm pretty sure you're autistic, you should go talk to these people for a proper diagnosis" and I never did.) Occasionally the idea resurfaces (and is again at the moment, to some degree, because I'm having problems at work that are surely neurodivergence related) and I end up dropping it. Mostly, as far as I can tell, as an adult who is able to live independently, maintain employment, and isn't going to return to education, there really aren't many/any resources out there, so it feels a bit pointless. Some people do get a lot of benefit from the confirmation/certainty that comes with a diagnosis, so you may feel a diagnosis is worthwhile for you, even if it doesn't get you access to any concrete resources. I can't decide if I'm one of those people or not, to be honest.
Now, there are concrete downsides to diagnosis--some countries will use an autism diagnosis as grounds to deny a visa; in the US it's not an unrealistic worry that it'll make accessing medical transition harder if you're trans; I have a friend who has come down on the side of "no official diagnosis" for fear it could jeopardise his access to ADHD meds in the future. (I picked up an ADHD diagnosis a couple years ago -- I'd been taking meds for anxiety and switch psychiatrists and they were like "Umm... I'm not saying your not anxious, but you're actually describing ADHD". I suspect my brain lies in the autism/ADHD uncanny valley. I mention this as a lead in to say that I don't share my friend's fear, but it's also not an unrealistic fear.)
I'm probably five years younger than you. We had rope climbing but it wasn't part of the Presidential Physical Fitness Award (which I am seemingly deeply proud of actually having managed in the third grade, despite being crap at pull ups, and I was even worse at rope climbing).
Are you getting hormones from a doctor? You should be able to ask them for a referral, either for a scan or just to a specialist if they're not the right person. (Unless there's something specific requiring a specialist, breast health screening is often done by GPs/primary care, at least in the US.)