This does not involve piracy, but it does break Epic's TOS lightly (use a secondary account).
No , you do not. Fortnite is a free-to-play game, and Nintendo does not require a paid subscription for free-to-play online games. fortnite switch nsp top
Players running custom firmware (like Atmosphere) often manage all their titles via homebrew installers (like Tinfoil or DBI), preferring a single local library of NSP files. This does not involve piracy, but it does