In a nutshell:
If I were setting up an exchange, I would look for a back-end that already exists, with a front-end that I could "white label".
Firstly, I am a developer that works with Bitshares, so my advice can be considered tainted. In my position, I know the code. I do not necessarily know the business. So take everything I say and place it in context.
Secondly, I know very little about the intricacies of laws in India, and I never encourage illegal activity. So make sure you what you do is legal within your jurisdiction.
Now, on with the show...
Bitshares: The Code
Bitshares-core is an open-source (MIT licensed) blockchain project that is based on DPoS (Distributed Proof of Stake).
Bitshares: The Network
Scattered around the world are "Witnesses". They take care of making sure the transactions coming through are legitimate. Think of them as "miners" in the Bitcoin world.
Where you may fit in:
What some have done is provide a "front-end" to the Bitshares blockchain. They provide the customer service, the wallet, the website, etc. Bitshares takes care of the network pieces.
I would strongly consider building it with Bitshares as the back-end. It provides "stablecoins" that allow fiat-like balances to sit there without exposing it to the volatility of crypto currency. It provides a trading platform with some existing trading pairs, and you can create your own. There are open-source front-ends that you can "white label"