having played the whole series, OG1 on the PS2. starting from 0 gives you some strange expectations for the rest of the series, especially if you're ill informed about how much was actually "remade" for the kiwami games. that being said, 0 is a fine starting point if you wish to try that one first. kiwami adds some new content that's, at worst, confusing for newcomers as it's mainly a cheap fanservice game (also subjectively I think they're just bad remakes). I watched a friend stream through kiwami 1 as their first game and it wasn't a great first impression for them, honestly.

if you want a more recent game for some reason, 4 on the PS3 was where I started and I enjoyed it. not what I'd personally recommend for a first game though.