The PS1 games (1-3) are still fun and play really well, but the dated graphics and controls might be too much for you depending on your standards.
Check out the YouTube channel Avalanche Reviews. He does some pretty in depth RE retrospectives that will answer all your questions.
Personally i prefer the RE1 remake thats on Steam. Its basically an HD version of the GameCube remake which IMO is the definitive version of RE1. Also gives the option for modern control scheme if you prefer. Same advice goes for RE Zero.
RE2 and RE3, the PS1 versions are still king for me. But the recent remakes are also great if you want a modern take.
Code Veronica, I'd play on Dreamcast, PS2, or GameCube. Whatever's most accessible.
RE4, the current remaster on Steam is fine and a great game but there's rumors Capcom is working on that one for the next remake so you might want to wait.
RE5, just play the Steam version. Steamworks got patched in a few years back.
RE6, Revolutions, RE7 - Play on Steam.
As for how to play, it varies by game but mostly you want to take out the zombies in your way but avoid and not waste ammo resources on the ones you can easily run past. You do want to manage your resources as well as possible, especially in the early games. This changes by RE4 where the series got its revolutionary shake up and turned more action-horror.