I need to set up a network with ten or more wifi connections in a motorhome with a bunch of iDevices, apple TVs etc. and want to have an outside web connection for all those devices. Most of the bandwidth will be internal data and not to/from the web. I can set up a personal hotspot but am limited to 5 connections. Is there any way to set up something like an airport express for all the wifi connections and have an ipad on the system as the only Internet connection, since the 10/100 of the hub will not be connected?
Unfortunately none of Apple's routers can use the iPhone or iPad tethering as a source internet connection.
It looks like it might be possible using certain builds of the DD-WRT custom firmware with the Linksys WRT160NL, but based on that link, it looks like it will likely require a fair bit of hacking, beyond just installing the custom firmware (i.e. it needs to be certain versions, and it looks like further drivers need to be compiled/installed).
If you have a Mac handy, you could tether the iPad to it (with USB or Bluetooth), then use the Mac's Internet Sharing to share to the other devices over Wi-Fi.
Alternatively, you could look into getting a 3G/LTE hotspot device from your wireless provider. It would likely entail some additional cost, but it would be most suited to what you're wanting to do. Some providers offer some data plan sharing amongst devices as well, so the additional costs might be minimal.