Multiple Network

Bit of a confusing one here, I have been using Home Assistant on an isolated student halls WiFi network for a while now and have just purchased some Xiaomi smart products. The products are not compatible with my WiFi so I had an idea to buy a mobile router and just enough data to set it up, with the long term aim of just having the router run with no data being paid for so it is completely local.

How would I achieve this with Home Assistant? It may make it even harder to achieve as I run Homebridge which would have to be on my main network in order to still use my Apple TV (Hub) as normal.

Thank you to anyone in advance! Just need a few pointers to get me on my way.