Noida first-timer: Sector 162 RBS Buildtech. What should I look out for?

Okay I'll be honest — I completely underestimated how confusing this first home buying process is. I'm a first-timer, looking at a 2BHK in Noida's Sector 162, specifically an RBS Buildtech project. It's under-construction and that makes me nervous. Log bolte hain delivery delays common hain. RBS Buildtech ka track record kaisa hai in Sector 162? How do you even assess the risk of an under-construction project? Also, property price ke alawa, kitna extra budget rakhna chahiye? Stamp duty, registration, interiors, society maintenance... I'm hearing numbers like 15-20% extra but not sure if that's enough. Kya unexpected costs hain jo nobody tells you until it's too late? Any tips for negotiating? Help a newbie out!