Originally Posted by deovrat

Taj looks spectacular either at dawn or at dusk, so make your plans around either time. I'd say going down from Delhi in the morning, seeing some of Agra in the morning, having lunch, heading to Taj at dusk and returning at night by the same train is very practical. The returning train picks you up at Agra at 9 pm.
Fare for AC Chair car is INR 515 and Executive is INR 1010. Child fares might be available, but if you book through foreign traveller quota, they might not be applicable and you might be charged full amount.
I'd suggest to book as soon as you can firm up plans, and never at the station itself. Bookings open 4 months out.

You can carry 40 kg per person in AC Chair Car by the book, but you will never be asked to weigh it so don't worry. As long as your luggage doesn't stop movement of people inside the coach, nobody will give a damn.