You can use macOS Keychain without using iCloud Keychain. You just enter the password entry in the login keychain. Should still work.
a) You could surely store the 1Password master password right in KM macro. That would be easier, but would be much less secure. Especially if you sync macros between machines as I do.
b) Not sure what you mean by this. Since 1Password already integrates with Safari, not sure what else you'd like to do. There are some topics related to this here on the forum. For example How to Search 1Password 7 and Open 1Password Mini