Hiader5, you have very rightly pointed out that availability of CNG is the biggest issue. Long long lines these days means you have to waste a lot of time in getting CNG unless you have 2 cars and a driver who can waste his time to get your CNG while you drive the 2nd car and get your work done.
Secondly, CNG works fine in most cars but really gives some problems to the electrical and mechanical systems over the period of time. Blown fuses, car refusing to start, build up on valves and cylinder heads, cooling issues etc. Its better to leave the new car on petrol and if you can afford it buy a 2nd hand car with CNG in it. That's my suggestion.