Buy 1 switch to hack. Run Homebrew, Android, Emulators, whatever.
Buy 1 switch to leave completely vanilla. This is for playing online, buying games from E-Shop. This can also be a massive help because you can use this un-hacked switch to transfer updates for games to your hacked switch over AD-Hoc. Makes it super easy to install OEM updates for games, rather than using homebrew to acquire these.
Grand Total: 2 Switches. 1 Hacked & Offline, 1 Vanilla & Online.