I can really only answer the first two or three as I was already on my own when I was out/transitioned.
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There's a lot of internalized transphobia that definitely makes this really challenging early on. I had a buddy who's dad loved to say shit like "I'm a teenage lesbian trapped in a man's body" and it always felt super icky. I definitely feel that ick waning as I transition, but there are still those "man pretending to be a woman" brainworms that bug me from time to time.
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I feel like at least half the trans people I know are on the spectrum, so you'll fit right in lol.
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I can at least give a bit of insight on this one, as I unfortunately hid things, just not from my parents.
Undergarments and women's cut clothes are really nice and not necessarily noticeable to those around you. It's subtle, but the difference between a women's and men's tee makes a significant difference for how I see myself, but others are unlikely to notice.
Growing your hair out is another possible option and did wonders for my mental health, while simply using the excuse of wanting to try something new or even just being too lazy/busy to get it cut.
Getting my ears pierced was another small thing that's pretty common with men too nowadays. Even clip-on earrings are an option if you want to go really incognito.
Tinted chapstick and similar "not-makeup" cosmetics are again, subtle, but they are small things that add up without being too overt.
"Feminizing workouts" sound ridiculous, but they can legit give you great hips/butt without hormones. Again, not anything super overt, but I guarantee you'll notice before anyone else does.