Ive checked the RFM69 and ive decided that iam not going to try it
But instead, if i read it correctly i can use an Arduino + (official) Ethernet shield as a gateway.
Domoticz supports multiple gateways, so i should be able to place an Ethernet shield on each floor and use the NRF's to each gateway
ill how that works out
BTW: this is an W5100 right?