Regarding Taxi service, you can get service of prepaid taxi service at New Delhi Railway Station with nominal charges. Also you can avail Radio Taxi Cab service i.e. Mega Cabs, Taxi for Sure etc. and can be booked online and they can pick you from station when your train reach. Now I always use Metro service as this is cheapest way and for metro you should need to visit Ajmeri Gate side of New Delhi Railway Station instead of Paharganj Side. After reaching your nearest metro point of your destination you can avail services of Auto Rickshaw to reach the destination.