switch RCM 准备
if you want unthethered CFW, keep FW as low as possible
If you want the chance to maybe, one day, not have to use a external device, then it is recommended to stay on a FW as low as possible. Beware that this means that you potentially need to wait for a very long time (months to years) for this to happen, if ever.
If your Switch is one of the older hardware revisions and you don’t mind having to use jigs/hardmods/AutoRCM and sending the exploit via computer, phone or dongle everytime you want to launch into CFW then it is completely safe to update.
Use emuMMC for offline CFW use
Atmosphere now supports emuMMC (emuNAND): a copy of Switch system software, run entirely from the SD card instead. This erases ban risks due to the fact that emuMMC is run in a quarantined, offline state, not touching the internal memory. You are still able to boot into original firmware to play online.
If you use an emuNAND for CFW and keep your sysNAND clean for playing online, you should use 90DNS on your emuNAND.
FAT32 vs exFAT
FAT32 is the safest, because exfat by default doesn’t have any security safeties preventing partition table corruption (you can read that on Wikipedia). And Switch OS has special function that can read folder with archive attribute as file, so it’s splitting >4GB files by default and put chunks to folder with archive bit even on exfat. So exfat doesn’t have any pros over FAT32 on Switch.
But Switch is formatting by default to exfat larger than 32 GB (iirc) cards.
Saves data are stored only in two places: internal memory and cloud.