Welcome aboard Salman.
Get your car tuned for Petrol first from a good mechanic. Get rid of all the issues, Clutch & Pressure plates are crucial for cars pick up. Then go to some CNG guy and ask him to perfectly tune the car for CNG.
This way your car will give you better response and mileage.
My Cultus gives me 120 Kms on every tankful of CNG (7Kg) with continuous AC usage. So yours should be similar too.
Also if you bought it just now, do change all the oils of the car, Engine Oil, Brake Oil, Gear Oil, and start maintaining history.
Always use good brands in Oil with 10W40 grade like of Liqui Moly, Petromin, CEPSA, Dextron, Caltex.
Secondly you can also use Liqui Moly Fuel System/Injection Cleaner for some improved performance right on.
Fog lights and other such decorative accessories can be get from Tariq Road car accessories market (before McDonalds). They will cost you from 300-1500 according to your likings. In my opinion, the 300 rupees one will do the same here in Karachi weather Only opt for better looking and durable one. All are Chinese stuffs.
Let me know if you require any other info...