Thank you for the thorough reply @mfalkvidd
I already had a look the pages you linked but some of the questions I had were only partially answered by those pages so I appreciate you taking the time to answer all of them.
Judging by your answers i'm not going to try two gateways. I will instead look into building an ethernet gateway or perhaps forwarding data from one controller to the next.
Signing is definitely something i want to implement too as my gateway seems to be picking up pacakges from a mysensors user near me!
Especially your statements about undefined behaviour in regards to ACKs were helpful.
Thanks again and apologies for replying as late as i did.