Wow - for the first time in years, I have to think to answer a question in here...
1. Might be detectable - although currently it seems not to result in any reaction by Nintendo. Easy answer would be "no, its not detectable".
No, Nintendos Bootloader does not remove AutoRCM - it simply fails to boot.
Which is the concept of AutoRCM. Nintendos Firmwareupdates remove it though - if you dont apply them with something like ChoixduJourNX (which has apply AutoRCM enabled by default - by default, because AutoRCM is also used to stop the Nintendo Bootloader from working before it burns fuses. Never forget, that AutoRCM is also used for that.
).
2. Should be safe. Depends on what you want - more on that later.
3. Either way should be fine. "Fake" Linking a Nintendo account can be done with either this method:
https://gbatemp.net/threads/any-way-to-edit-profile-and-fake-link-account.526255/ or via Kefir (
https://gbatemp.net/threads/kefir-updater.539086/ ). (Kefir should be more easy.
)
4. Yes. If its practicable is another question.
(5). Dont forget to setup 90DNS as soon as possible - even on stock firmware - and unplug your router from the internet while setting the entire thing up. Thats part of isolating emunand - so it never will be able to talk to Nintendo broadcasting several of your unique hardware IDs.
Reason to keep fusecount low: To be able to downgrade to 4.1.0 (at the moment), which allows for a tethered (WLAN - ) exploit to basically replace your injector dongle (or smartphone, or PC...) - and still be able to boot into RCM > hekate > CFW - See:
https://gbatemp.net/threads/caffeine-updated-to-support-fw-4-1-0-works-on-patched-switches.541826/
You'd still need a WLAN connection (with 90DNS set up, so it doesnt pull updates) presumably - so its tethered - but it could be tethered to your smartphones hotspot - f.e.
Short answer - dongle still is more convenient for most people.
Reason to update to most recent Nintendo firmware in 'real nand' (if also using emuMMC) - to be able to play online. (While still be able to use emummc (emunand) - if your switch is an unpatched unit, that allows you to enter RCM Hekate via payload injector) 'Fake Linking accounts' can be done via other means, so thats not a reason.
Please doublecheck - if autorcm on "clean stock nand" doesnt result in a ban - my answer here was only extrapolated - not based on actual knowledge.
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Yes, if you stayed at 4.1.0 or below. No in all other cases.
For yes - see:
https://gbatemp.net/threads/caffeine-updated-to-support-fw-4-1-0-works-on-patched-switches.541826/