First-time buyers in Greater Noida: what did you miss?

Visited CGEWHO's project in Sector 140 last weekend. Builder ne jo price quote kiya, uske alawa aur kitne hidden costs hote hain? Matlab, stamp duty, registration, aur interiors ke liye kitna buffer rakhna chahiye? Also, first-time buyer hoon, site visit pe kya important cheezein check karun jo builder nahi batayega? Thodi practical advice chahiye.