First home in Gurugram, feeling lost on hidden costs and site visits

Budgeting for your first home is way more complex than just the property price, honestly. I'm looking at places in Sector 37C, specifically some Indiabulls Estate projects, and it feels like the total cost keeps climbing. Everyone talks about the flat price, but no one really warns you about stamp duty, registration, PLC, and then interiors. My parents keep saying factor in at least 15-20% extra, but ab samajh nahi aa raha if that's enough. Also, for site visits, what are the absolute must-ask questions? Beyond the usual amenities, what red flags should I be looking for that builders won't volunteer? Like, is there a checklist for things like water pressure, mobile network, or even the quality of the plaster? Has anyone else felt totally overwhelmed by all these hidden costs and things to check? It's a lot for a first-timer.