it has a camera and microphone, so can you actually do video calls?

I don't think any of the T-Watches have cameras. But you're right about the meshtastic bandwidth, it's more for some simple messages.

So if the network isn't great here I assume I can put up my own node.

Yep, and a node is just another LoRa device, like the T-Watch. If it's just near your house, it should work great. My Wio Tracker L1 picks up a repeater on the other side my suburb, and that gives me some crazy range.

It doesn't sound like you do, but if you need intercity range, LoRaWAN might also be worth looking into. In Queensland, many city councils (Brisbane, Gold Coast, Moreton Bay) have their own LoRaWAN networks that peer with The Things Network, and you can integrate it with Home Assistant using an integration, or my preferred way is through MQTT. You would probably have to write the firmware yourself with this option though.