This question doesn't got much attention. I hope to get some details here.
What do I need to know to build a gateway with an Arduino Ethernet Shield?
Anything special or can I just put the shield on the Arduino and connect the NRF24L01 radio according to the table?
Yes, I'm using an ethernet shield too. Just follow the instructions.
Yes, just stick it on your Arduino and your good to go.
I did have to change the pin configuration with an Arduino Mega2560 and the ethernet shield. I've placed a comment with my pin config in that tutorial.