So hey,
just as an update on this stuff; inviting my Mom over for lunch, and coming out to her afterward went pretty well!
The Yakisoba part took time. Lots of veg to prep, and we kept getting distracted. But
we ended up making a pretty tasty meal, even if it wasn't very pretty, and even with the low-sugar and low-sodium requirements. Had enough leftovers to send home for my Step-Dad too. Mom brought a tasty lemon coconut-flour cake she'd made for desert, and a cute little Sushi themed card game for us to playtest. All in all, it was a pretty good time!
I'd already told her that I wanted to have an important conversation afterward, and she always sorta knew something queer-ish was up with me, but didn't know to expect I was Trans and NB. Her exposure to gender stuff is pretty minimal, so I went through the whole "Differences between Sex and Gender" talk. She asked about if that meant I'd dress differently, or if dating one of my lesbian friends was on the table now, or if it was expensive, or if I'd want to do stuff to my bodyparts, etc. She was generally pretty quiet, but supportive. She did point out how she had started to notice my looks had changed, and asked if hormones had affected my voice too (so guess I'm making some progress on voice training :3). We talked a bit about the psychological changes, the motion-sickness, the moodiness, and all that. Spent some time talking about history, the gender policing I got that made me clamp down on it, the handful of complications it's brought to former friendships, and the little hints I never knew what to make of when I was younger. She mentioned how much happier and more present and in-touch I seemed in the last year or so too, and was glad that this process has helped me out so much.
On the flip-side, she hit a pretty hard hangup with pronouns, and totally balked at using They or She (said she'd just use my name). I probed her a bit about it, and she said that she'd always think of me as her Son, which stung too... but then sorta corrected herself and said "Well, no. I always talk about [Older Sister] as my daughter, and [Younger Brother] as my son, but I've always said [Solifuge] is just [Solifuge]," so there's that I guess? She asked what she should call me as to our relationship, and I just pointed out that I'm still her kid, or her child. She did say she wanted to be supportive here, but needed time to process it all. We cleared up who all knew in the family, and talked a bit about why some people don't know already, and our read on how supportive they'd be. We basically agreed across the board on where the landmines were, so... that'll be a fun bridge to cross when we come to it.
Anyway, she likes reading in her downtime. To help with some of the hangups, I'd like to try providing her with some helpful literature about being a Trans Ally next. She's probably going to be one of my major supporters in this, at least within the immediate family... so I'd really like to help her understand the situation better before charging on ahead. But all in all, it was a good experience, with a better-than-expected outcome.