Hi Neel,

This is a unique project for a business analyst, since I would think they would normally have someone on the dev side handle this. But your BA skills apply none the less.

Start with the As-Is Stack:

• What is used today?
• What are all of the applications and systems that map to each piece of the tech stack? 
• What are the benefits realized by the existing pieces of the stack? Speed, Scalability, Interoperability (you will likely uncover a lot of non-functional requirements here).
• How does the current stack meet the needs of the organizations, its high-level goals, and its business strategy? Are there clear short comings of a particular technology being used?

Determining the To-Be Stack will depend on the requirements and shortcomings you find in the As-Is state.

If I was given this project, I'd look at it as a fun opportunity to dive in and learn about the technology side of the business which business analysts are often excluded from.  Fun!

Chris