Need advice for buying home with full payment in RERA registered under construction project

There is a residential project in Panvel that I am interested in buying a home to get settled. The project is registered in RERA and HDFC, Axis bank had cleared the project for loan (I have my cousin in HDFC loan dept who confirmed this). Currently only excavation work is going on and possession in by end of 2026. The builders previous reputation is good (no problem with any previous projects). I am not hesitant for going with the deal because everything looks clean, I just want to understand what are the things that could go wrong in an unfortunate situation. I am willing to pay full amount (almost 90%) and book at a discount price with registration. Will it be okay? The sales team is insisting me to go for allotment letter and do registration later only. They mention that allotment letter confirms the exact floor and room number I have booked and its a solid proof. The team I am dealing with is a mandate team assigned by builder for their marketing. The developer is a partnership LLP registered company. I am not an investor I am buying my first home with my years of savings. I am confused. What do you suggest.