how to Install an app and afterwards have the initial configuration screen (as a new phone)? How may i install an app, and have the "startup configuration screen" (where the user selects his language, google accounts, etc) without doing a factory reset?
You can make that app an system app that will prevent your end user from uninstalling this app and even after an hard reset the app is still active, plus the app is installed before the device is given the end user.

ps you must modify the system for that which will mostly cause a loss of warranty.