Not sure which path is best. not sure where we're at for downloading switch DLC and installing it from sd, if that's what you're asking.
but
if you have not done any hacking/homebrew/cfw, then use CTCaer/hekate only to backup properly (look at the sticky about switch banning for full details on how to)
Restore to this clean backup before going online if you've used ANY hacks/cfw/homebrew
Once you go online, you must create a NEW clean backup . Stay offline and hack away, but you must restore from the most recently created "clean" one if you want to go online again.
If you're trying to save fuses, I'm not sure the current knowledge of detection of burnt fuses or not (check the switch banning sticky for info on this too)
Thinking is, Nintendo changes certain info in files whenever they talk with your switch/you go online, so if there's a discrepancy between their files and yours, you get banned. SXOS backups aren't as clean as CTCaer/hekate, so use CTCaer/hekate to create a completely clean backup before using SXOS (or other cfw/homebrew tools).
As far as advice goes, I'm not sure how to figure out DLC. I'm guessing in a little while it'll be easy enough to just install it directly from sd after getting it from somewhere on the web.