Given the proliferation of AIS-equipped VHFs, I though of another caution.
I tried using two VHFs, both with AIS, and both on N2K. I ended up with issues because vendors don't seem to agree on how to handle multiple AIS devices on the same network. I couldn't turn the AIS reports on/off on N2K at the VHFs, and the various displays that show AIS targets can't be told which AIS receiver to listen to. Confusion reigned. And AIS reports take up a lot of network bandwidth, so you really don't want more of them running than needed.
I ended up changing both VHFs to non-AIS versions so the only AIS device was my transceiver. Now everything works, but I've got no backup if the main AIS dies.