I can't speak to your first question, but to the second question, the only version which will auto-update is the Steam version. If you want auto-updates, you should get the Steam copy. Also keep in mind, that the Larian Vault is likely to be the last place to get updates. Their focus will be Steam first (because of the simplicity in submitting updates on their end), then GoG (because of the userbase size) and finally the Larian Vault.
Using the Vault usually gives you a Steam key too and I assume that even if you choose the DRM free copy you still get the Steam key (two in case you ordered the CE)
I assume that this goes for any extra copies from KS as well if you choose the Vault for them (Vault + Steam/Gog key)
