Lack of trustworthy reports doesn't really help determine whether using full online dumps is safe or not, so I'd say it's better to be on a safe side. Do your own research, check with people you trust and make a decision yourself.
Unfortunately, I don't know anything about that. Someone else might be able to help you out. I'd check
this thread for more info.
Unfortunately, it won't wipe telemetry logs because, as far as I know, factory reset clears the USER partition of the sysMMC, not the SYSTEM where telemetry is being stored. But even if you do wipe all the telemetry and connect to the Nintendo servers at some point later on, it would cause a log mismatch and flag you for ban at best. The best case would be if it was possible to check what logs Nintendo has of your console and to erase them up until that point in the past only or block telemetry altogether without blocking anything else (e.g. eShop access, NSO, etc.).
The only way to "clear" the telemetry after you've done some hacking and stuff and not get banned in the process of doing so is to make a clean backup of your sysMMC
before you do something you shouldn't usually do, including risky stuff like online dumps for the MIG Switch and alike, and restore it
only if you've
never connected to the Nintendo servers afterwards (stayed offline, used 90DNS or DNS MITM). Unfortunately, if you don't have a modded Switch, you can't do it unless you mod your Switch first, therefore using risky dumps on a MIG Switch on an unmodded Switch is something I wouldn't recommend unless you don't mind getting your console banned or it's already banned. Or modded, but then again why do you need a MIG Switch on a modded console? Only if you'd like to play your own backups online on stock firmware, while leaving all the hacking stuff to the emuMMC, I guess.
MIG Switch is 2nd best thing for piracy on all but unpatched Switches (ipatched, v2s, Lites and OLEDs), modchip being the first of course. Having a modded Switch as well makes updating games somewhat easier (matching the versions locally).