1) You can use your own currency symbol and set it within the ClassiPress admin dashboard, however collecting payments in that currency depends on the payment gateway.
2) The default payment gateway which comes with the theme, PayPal, does not support INR, however you can purchase
other payment gateways from the AppThemes marketplace, and
2checkout.com for example, does support INR.
3) If we're talking about a search based on the custom fields input into the ad listings, this is already available in the theme as shown
here on the demo site (ClassiPress allows you to create custom fields for various category listing forms). Outside of this, it would require custom coding. Thanks.