When it comes to input "best" is highly subjective, but with that said: Just adding Japanese support in the system language settings is fine.

Standard Qwerty keyboards are well supported, you'll need to either check the key shortcut to switch between inputs or do it with the mouse if it's infrequent enough.

People using it daily will tweak a lot more, have a straight to IME and straight out of IME key instead of the default switching pattern, potentially add more tweaks to always have half-width space and ponctuation whatever the mode they're in etc., but that's a rabbit-hole you'll be free to fall into.

BTW the reverse works well enough: Windows has a specific mode to force US ANSI on JIS layouts and still use the additional japanese keys. Kinda fun they felt the need to leave that mode in.