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.I came across an article recently where a fella in a UK model railway club had used either Arduinos or Pis (I don't remember which) extensively on a layout. It worked well until he took the layout to an exhibition where there was enormous amounts of 'interference' which had the effect of crashing the system. Apparently, each of the devices had their own Wifi module and became overloaded (and crashed) by all the mobile phones at the exhibition which were polling to make contact.
Going forward, I think solutions to this issue need to be found. I'm not sure that every device on a model railway necessarily needs to be connected to the internet. A safer solution might be to have them all on their own private network communicating with a suitably 'beefed up' base station. The base station could connect to regular wireless. Of course, this is a 'hub' type arrangement as opposed to a true IOT configuration, but if interference due to use of a common network is causing a problem, maybe it isn't the way to go.