I created a register form with the custom fields using shortcode [mb_user_profile_register id="user-custom-group"]
But I'd like to put in first position the custom fields instead of comon fields like username, enamil etc.
There isn't an option to add the custom fields above the default fields in the form. You can try to use the filter hook rwmb_profile_register_fields to modify the default fields and add your custom fields there.
I'm afraid that there isn't an option to auto-login for the user after creating the account. I will inform the development team to consider supporting that feature in future updates.