As the fair area is really big, if all the halls a...

As the fair area is really big, if all the halls are full and you will be interested in each stand, you will walk a lot.
There are plenty of rest areas inside, and classic is more expensive than that. If you need this, you will spend 3 euro.
You can go by metro number 51 from the center, there are 8 stops in between. You can buy a single-use (hourly) ticket for 3 euro on departure and return or you can buy one OV card from vending machines and use it just like Istanbul card. The fee for this card is 2.16 euro, but you need to pay 7.5 euro for the card. The card is more meaningful and practical if you are going to do it for 4 days because you can wait in the kiosk press queue to buy tickets at rai station.