Of course you could use rpi as gateway, but as personal advice I'd suggest to get some mini pro as sensor nodes and keep the Uno as the gateway or the prototype platform. The most flexible solution would be to make an mqtt ethernet gateway and use rpi as mqtt broker and controller with openhab or whatever else you like, since the mqtt in the middle allows also to have multiple controllers. I also wanted to try openhab and tried openhabian but it turned out to be too complicated, so I moved to domoticz and it was much easier to put things together.