Thank you everyone for the help, for a used car kayaba shocks were too expensive for me so i replaced them with kabli ones and he gave me a year warranty. Till now drive is smooth and much better.
As for downpiping i got the straight piping done. But he did put one custom made small dholki in the middle. He made it himself and said its an open type and will give you less noise as i wanted but will provide good free flow as well. And surely whatever he did works because sound is good, not loud and when i pressed down the accelerator previously i felt like something is stopping the car for taking pick, but now it gains speed very quickly.
Does free flow effect CNG / petrol consumption?