i have one. love the beast.
1. 300K easy life on engine. just maintain it, oil change etc. later just add new rings. make sure you chnage the timing belt around a 100K. get valves adjusted too.
2. CNG is fine. just run it on petrol for half a tank when cng finishes once a month.
3. suspension life with cng and hard use, about a 100K. add one leaf spring each tyre if it settles. it cost me Rs. 1000 a week ago. otherwise you will pay for new front tyres and joints. i have this happening.
good luck bro.