Visited Anant Raj projects near Gopalpur – my first property dilemma

Visited a few Anant Raj projects near Gopalpur last weekend, looking for a 2BHK. My first property hai, so thoda nervous hoon. Builders quote base price, but all these extra charges like PLC, stamp duty, registration, maintenance advance, it's so confusing. How much extra should I realistically factor in for the *true* all-in cost? Is it like 15-20% above the base price? Also, super area vs carpet area ka chakkar samajh nahi aa raha. Builders seem to inflate numbers a lot. How to ensure I'm paying for what I actually get? Aur construction-linked payment plan ya down payment option, which is smarter for an under-construction project? Koi experience share kar sakta hai?