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.
