I often use Shirobon's serum preset pack when making music, it has some really nice sounds https://shirobon.bandcamp.com/album/shirobon-presents-chiptune-for-serum
Aside from that, I also sometimes use some free/cheap chiptune VSTs like ymVST and Peach
For sound effects specifically, Bluchu showed me this tool that seems pretty handy, I'm going to play around with it some more https://iznaut.itch.io/bfxr
Good luck! :D