Mileage - depends on your driving style, traffic conditions, so on. The owners have different experience.
Performance - again, depends on what you have driven before (what do you compare with, basically). I my personal opinion, it is a very good car for city driving.
Accessories - depends on what you want, and how much you can spend! Differentiate between 'need' and 'want'
As you see, my response is along your personal preference. Please research online for all this before you decide. It gives you different perspective, which would help you decide. You will see that the opinions differ due to individuals perferences.
You will have to check twice before the delivery - once before registration and next before you taking delivery (also known as PDI - Pre Delivery Inspection). Broadly, before registration check for interior/exterior finish, any dents/scratch/damage, under the hood, cross check engine/chassis number, so on. Post registration, you can focus on features and functionalities of the car.
Message me (PM) and I shall share you a checklist which I found online (created by someone else, not me btw