You can automate at least some of this with `defaults write` commands or copying files to the right places. If you look at what some existing MDM platforms do you should be able to do this a lot more efficiently.
defaults write only works after you have shell access, which means Setup Assistant is already done.
There are tools that modify marker files like .AppleSetupDone via Recovery Mode, but that's mainly for bypassing MDM enrollment on physical Macs - you'd still need to create a valid user account with proper Directory Services entries, keychain, etc.
The VNC + OCR approach is less elegant but works reliably without needing to reverse-engineer macOS internals or rely on undocumented behaviors that might break between versions.