It would be hard to give any verdict on the fuel type as the car is still in the queue to get launched. So we would suggest you to wait for the official announcement from the brand's side.
It would be unfair to give a verdict here as the Tata Hexa is not launched yet. So, we would suggest you to wait for the official launch and stay tuned for future updates.
For the availability and prices of the spare parts, we'd suggest you to connect with the nearest authorized service center. Click on the link and select your desired city for [service centers@https://www.cardekho.com/Tata/car-service-center.htm