Greater Noida flat: under-construction delivery tension & hidden cost shock

Been looking for flats in Greater Noida for a few months now and honestly, bahut confused hoon. Airwil Group ka ek under-construction project pasand aaya hai Sector 25 mein. But delivery risk ka kya karein? Koi experience hai toh share karo. Also, property price ke alawa aur kitna budget rakhna chahiye for stamp duty, registration, interiors, etc.? My parents keep saying it's a lot, but I had no idea. Kya cheezein dekhni chahiye site visit pe? Any hidden costs I should know about? Ab samajh nahi aa raha.