Thanks for purchasing the theme. Sorry that you’re having some troubles modifying the theme. The answers to your questions are given below:
To add new registration field you need to modify it on the theme core maybe on a child theme. You can override theme functionality on child theme easily.
To customise the ads post form you need to modify the template itself. Copy the ad posting template & then paste it on child theme to modify the fields accordingly.
To integrate SMS OTP system you need to integrate this part actually. We don’t have option to do that automatically
Location is already added. With the proper GMAP API the fields will populate automatically that’s how it works actually.
To show the map of seller its a custom job to do need to modify single ads template in this case.
Referral is not available by default but you can maybe use post affiliate pro like plugin.
I think by seeing your query these are not out of the box thing within the theme & you need to customise accordingly. Hiring a developer would be nice in this case.
Let us know if you need anymore help in this case.