Hello Darshan,
I would recommend that you spend the time solving the errors in MxModelReflection as it's used by a lot of modules so it might come in handy later.
Not sure if the OAuth module will work without it, but of course you can try and make your own implementation of OAuth or change the module, there's no need to use the module, it's just an easy to get started package that might come with updates later so it saves you a lot of time.
As for the adapt or create statement, you'll need to set up your config so a microflow is called on resolution of the OAuth call. So once the user is authenticated against the IdP and you get the response back, the OAuth java code will call the microflow in your config with a User parameter, at which point you can log them in - this is if I remember the above correctly.
Hope this helps.