I have a Gateway displaying data from a weather sensor Node. I also have another Gateway displaying different data from several soil moisture Nodes.
Are there any "good practices" about when to set up separate Gateways/Networks?
There certainly are a wide variety of practices, but I'm not sure there is a 'right' one. I think, first and foremost, separate gateways should operate on separate networks, simply to keep the traffic limited on each.
But why have separate gateways? Well, if you have distinct 'regions' on your property that are widely separately physically, having a gateway for each region is a good thing, keeping the distance from node to gateway within reachable bounds. Also, if you have separate 'logical' regions, you might have multiple gateways - in my case, I have a 'household/landscape/ gateway and I have a 'workshop' gateway. This keeps my Dust Collector Remotes off the household network and localized to the workshop where they belong.
This then brings up the pragmatic approach to the question. If I want to install a mailbox monitor, it's too far away from the household/landscape gateway unless I do something drastic. However, it is well within reach of my Workshop gateway. Guess which one I'll use...
UPDATE: one more thought, since the backend of both of my gateways is MQTT messaging, it doesn't really matter which gateway a node is connected to, all messages will get funneled through the central MQTT broker anyway.
Tom