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.
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
As of now, the brand has not made any official announcement on the price of Hexa but we can expect it to be around Rs.14.00 Lakh (Ex-Showroom). Stay tuned