2.4GHz Wi-Fi is too crowded for exhibition use, if you are going to use Wi-Fi it has to be a 802.11ac or newer 5GHz router with beam-forming (the type that has at least three aerials). Fortunately the new Pis have 5GHz Wi-Fi so can be used, but otherwise you will be best using a more resilient wireless solution such as Zigbee with a gateway to Wi-Fi.