Noida Extension flat: extra costs I didn't budget for

Honestly, I had no idea kitna extra kharcha hota hai beyond just the flat price. I'm looking at a 2BHK in Noida Extension, like Nimbus Realty ke projects near Sector 31. My budget is around ₹70L for the property value. But ab samajh nahi aa raha ki aur kitna buffer rakhna padega for stamp duty, registration, interiors, wiring, sab kuch? Builders toh bas basic price bolte hain. Also, under-construction properties mein delivery risk kaise evaluate karte hain? Nimbus ka track record sahi hai ya nahi, I'm not entirely sure. Site visit pe kya specific cheezein check karni chahiye jo sales team usually nahi batati? Like actual carpet area, wall finish, plumbing quality, you know? Any advice from experienced buyers would be super helpful.